Sticker
Details on a Transformers toy that are not molded, printed, or painted on may be provided by the application of one or more stickers - also known as labels or decals.
Stickers are a flexible substrate with colors and designs printed on one side and an adhesive substance on the other. Generally they are stuck to a wax-coated protective sheet before use, with the individual stickers being die-cut from a single sheet of backing while attached to this waxy sheet. Many toys have stickers already applied to them at the manufacturing plant.
Stickers were abundant throughout the first decade of the Transformers franchise, but since then have been effectively replaced with other detailing methods. Stickers still see some use today, but are mostly relegated to more "nostalgic" collector-oriented releases, and the occasional "there really is no better cost-effective option".
Use in Transformers
Generation 1
When the original Transformers toyline debuted in the early/mid 1980s, stickers were already an industry standard for larger toys. Vehicle-heavy action figure lines, like Star Wars and G.I. Joe, made extensive use of stickers on flat surfaces to provide more "realistic" detailing wile keeping production costs down. And as larger Transformers toys were already using other cost-saving measures to keep the price reasonable, stickers were used to ramp up the toys' detailing.
For the first several years of the line, shiny foil-based stickers were the norm for smaller details, with paper-based ones covering larger expanses of flat plastic. Most toys had a few stickers that were pre-applied at the factory (notably the big paper decals mentioned prior), supplemented by customer-applied stickers that came on a single sheet. By and large these stickers were used to add "tech" detailing to the robot modes, with some needing stickers to replicate more complex detailing in their alternate mode, like Soundwave's tape-player-mode text and power light. Rubsigns were introduced shortly after the line's debut, heat-sensitive stickers that changed colors, in this case revealing the robot's true allegiance (and marking the toy as an "official" Transformers brand toy).
As the line slowly ceased to be the unstoppable sales juggernaut of its early years, several cost-saving measures were taken, experimenting with ways of replacing or altering stickers. Several of the last-year Mini-Cassettes switched to detailed tampographs to replace the foil stickers that made up their "cassette" side/mode. But for most of the rest of the line, stickers stuck around (ha), but changes were made to the types of stickers used. Rubsigns were dropped altogether by the line's fifth year, and the Pretenders experimented with clear-plastic stickers that used less paint. This experiment was short-lived though (see "Pros and cons" below), and by year six, most new toys had moved to using cheaper, less durable paper-based stickers, which would persist to the end of the line. There were a few standouts, such as the individually-carded Action Masters having foil-like faction symbol stickers, and the water-play-based Aquaspeeders and Stormtroopers of the late European-market line used classic foil stickers (for hopefully obvious reasons), but exceptions from laminated paper decals were rare.
It's important to note that these changes were global, affecting all three major markets (US, Japan, Europe) at the same time.
Generation 2
The first year of Generation 2 in both the US and Europe was almost wholly recycled molds, and thus stickers were still the norm. Virtually all of the new-to-the-US-mold toys, such as the Color Changers, were originally from the prior year's European toyline, which -despite the use of new faction symbols- was still "Generation 1". Some used foil stickers (Aquaspeeders/Stormtroopers, Axelerators and Skyscorchers), while others kept with thick paper (tank Megatron, the Lightformers, Trakkons and Obliterators), albeit with stronger adhesive than the Japanese paper-decal toys just a few years prior.
By the second year of Generation 2, the apply-your-own separate sticker sheets vanished almost completely. Most toys still used factory-applied paper decals, but paint operations and tampographs became more and more commonplace. Even the recycled Aerialbot and Combaticon toys lacked separate sticker sheets (as did the ultimately-unreleased Protectobots and Stunticons). By 1995, many toys had eschewed sticker detailing altogether.
The only late Generation 2 exception to the "no separate sticker sheet" rule is Laser Optimus Prime, 1995's big-ticket item, which also featured a lot of "random robot mode tech greeblies" sticker detailing that called back to the early days of the line. Japan also brought back separate sticker sheets, though in a much more low-key manner; their releases of the Autobot Cyberjets each came with a separate transparent-plastic sheet full of extra detailing, including "battle damage" markings. It appears, however, that no instructions were given as to where on the toy these decals were supposed to go.
The "Beast era"
Starting in 1996, the rounded and organic sculpting of Beast Wars toys made even factory-applied stickers impractical... plus the toy industry had largely moved on from sticker use in general. That the first year toys eschewed any form of faction symbol on the actual toys also made stickers largely obsolete.
Stickers returned for the line's second year in a familiar form: the "energon chip", a tiny, often-hidden heat-reactive sticker that would reveal the robot's allegiance, bringing back the classic "rubsign" gimmick. These stickers stuck (ha ha) with the line up through the third year, but were replaced by the snazzier-looking "spark crystals" of the Transmetals 2.
In Japan, Beast Wars II made ample use of molds developed for Generation 2 in its early Destron releases, resulting in a fair amount of factory-applied paper stickers on toys like Megastorm, and Starscream & BB. In 1999, Metals Jaguar not only had a factory-applied sticker inside an opening chest compartment (revealing a Predacon faction symbol), but also the first separate sticker sheet in a Transformers toy since 1995. This foil sticker sheet featured two replacement "viewscreen" images for the chest-sticker (Generation 1 Megatron's head, and the classic Decepticon insignia on a purple grid background) as well as two Predacon symbols and two Decepticon symbols to be placed on his biceps as you wish. Mind, due to the rounded biceps, they don't really stay on well. The redeco of this toy, BotCon 2001's Transmetal Tigatron, also had a similar decal sheet.
Stickers made a very brief comeback in the short 1997 Machine Wars series. The Basic-sized figures had factory-applied paper stickers, while the larger boxed toys retained apply-your-own paper sticker sheets, as those toys were all redecos of older last-year-of-Generation-1 "transitional" European toys. In many cases their new sticker sheets yielded unimpressive or confusing results due to sticker sheets that no longer made sense with the new toy color schemes (i.e. putting a featureless white sticker onto a piece of white plastic of the same size and shape).
Beyond the beasts
Although Transformers began to shift back to predominantly "realistic" modern vehicle modes come the turn of the century (*deep, beleaguered sigh*), stickers remained rare as advancements in painting and tampographing techniques made the stickers increasingly outdated. Not gone, but definitely used sparingly and selectively at best.
The most common use of stickers over the following decades (*deep, beleaguered sigh*) has been in the repeated revivals of the rubsign gimmick, in lines like 2006's Classics and the 2010 Transformers series's "Reveal the Shield" subline. 2015's Robots in Disguise line had a similar sticker-based faction symbol gimmick, where each toy in the line had a sticker with a unique circular "code" surrounding the character's faction symbol, which unlocked them in the mobile game (now defunct); the Takara Adventure version of the line had a similar gimmick, only it was used to keep a "virtual checklist" of toys (also now defunct).
Stickers are often used to give toys a level of fine detailing that even current tampographing would not be able to provide (at least, for a reasonable cost), such as on "video screens" like the ones on 2003's Masterpiece Optimus Prime's flip-up forearm "communications screens". Numerous Real Gear Robots who transform into mobile phones, camcorders, handheld video game consoles and the like also make use of big chunky stickers for their on-screen visuals, as do the "spy tablet" modes of various former-cassette characters in the Titans Return toyline. Rescue Roy and the other 1-2-3 Transformers toys use stickers for their detailed department badges and such, a slightly odd choice for a line of Tonka "tough play" style toys for the younger set.
On occasion, stickers are used to cover areas of unpaintable plastic that would end up unsightly in one mode or the other, such as on the 2003 Official Transformers Collectors' Convention exclusives Sidewsipe and Sunstreaker, whose white plastics left a big patch of white on the roof of their red and yellow car modes.
In more collector-oriented lines, sticker sheets were sometimes included with some toys to bring back that old nostalgic "finalize/customize your toy" feel. The Takara Binaltech line (their name for Alternators) and its spin-offs had several toys with additional sticker sheets: most notable is the Kiss Players army-builder bot Autorooper, which came with a sticker sheet full of squad markings, enabling you to have your Autorooper be any of the forty-eight individual units from the story, not simply the one assigned to Atari Hitotonari, its pack-in "partner". (It is unknown if anyone actually did assemble a full compliment of Autoroopers. And if they did, what the hell they did with the other forty-seven Ataris. Though forty-eight Kremzeeks sound pretty awesome.) In 2013, the massive Generations: Thrilling 30 Titan Class Metroplex toy used over one hundred customer-applied stickers for detail to accentuate his bigness, presumably because doing all those fine details in paint would have skyrocketed the budget of this already-expensive figure. Other Titan Class toys like Fortress Maximus and Trypticon had similar sheets as well. BotCon would go to the customer-applied-sticker well repeatedly, mainly with the "customization class" exclusives, but they offered sheets for numerous other toys in their last year of operation.
Once in a while though, a toyline would make stickers a "thing" again. TakaraTomy's version of the Prime toyline actually took away a lot of the painted detailing of the Hasbro versions and replaced them with customer-applied sticker sheets. This was part of the line's "Arms Micron" gimmick, where each toy also came with an unassembled (and unpainted) Mini-Con still on a sprue, making the whole purchase more akin to buying and finishing a model kit. The Titans Return and Power of the Primes toylines featured factory-applied foil stickers on numerous larger Voyager and Leader Class figures... which actually did not go ever well with fans (see "Pros and cons" below). The following lines abandoned stickers once again.
Modern Generation 1 reissues & redecos
Reissues and redecoes of Generation 1 molds naturally retained their separate decal sheets, but as time went on, more and more began replacing factory-applied stickers with more durable tampographs. The most notable examples are in the reissues and redecoes of the original Sideswipe mold: the rally-deco headlamps on every use of the mold since the "New Year Special" release in 2002 have been tampographs.
The Takara Micromaster series (also begun in 2002) used nothing but paint operations for the five Micromaster six-teams, often leaving areas once covered by more complex-detail stickers blank and adding entirely new detailing to other areas. However, the final releases in the series, the "DX Micromaster" versions of Multiforce, used factory-applied paper decals for their robot mode torso detailing.
Pros and cons
A distinct advantage of stickers over paint in general is the ability to do much more intricately-detailed, multicolor detailing for a cheaper price. Many fans also enjoy the simple act of applying stickers, adding an almost personal touch to the toy upon ownership.
But, well... there are some disadvantages to them too. Okay, a lot of disadvantages.
Stickers are a common area for early wear-and-tear, as the designs can be abraded away, leaving ugly residue underneath. Some toys have stickers meant to be applied to areas all but guaranteed to destroy them by simply transforming the toy, one of the most notorious being the thigh stickers on the original Generation 1 Hot Rod. While the later Targetmaster Hot Rod used smaller thigh decals, scraping was still a problem. Paper stickers can lose their clear-plastic top-layer, making the paper underneath much more vulnerable to damage, plus they are (obviously) more susceptible to water damage, so no tub-time play!
While the transparent-plastic decals of the Pretender era are probably the most resilient to physical damage, they have their own problem, namely that even the color details tend to be semi-transparent, which can lead to the details getting lost should the sticker be applied to darker plastics. Also, any dirt that happens to get under the sticker becomes much more visible, and discoloring has been known to happen. Foil stickers have also been known to simply fade, losing their color details without the sticker below being scraped.
Just how "sticky" a sticker is can also lead to problems, especially when taking into account the materials they're made of and the surfaces they're meant to cover. The paper decals used on several toys in the Victory line and beyond in Japan had notoriously weak adhesive, meaning stickers wouldn't stay on terribly well. This was especially problematic with stickers meant to bend around corners or rounded surfaces, as the thickness of the paper made them more likely to come off on one side. The 20044 e-HOBBY Detritus toy (see left) suffered similar issues. Even foil stickers can have this problem, the most notorious example being the ridiculous "eye" sticker on the original "Seeker"-style jet mold that was supposed to go over the bridge of its nose, though several Diaclone molds wanted you to fold stickers at a 90-degree angle. The original Skids toy does that, plus has the problem of the instructions telling you to place circular stickers over the rounded screw-heads on his shoulders, which actually stick out beyond the background plastic of the shoulders! There's almost no way those are going to stay put, even if you never ever rotate his shoulders outward. Add in that his upper-thigh decals are much too easy to place in a way where they scrape against his crotch-plate when transforming, and you've got the triumvirate of Sticker Placement Annoyances.
And bringing back the "apply it yourself" angle, this often causes minor issues when buying old toys secondhand. More often than not, these stickers were applied without a lot of care by little kids, which mean stickers can end up misaligned or just flat-out in the wrong places. The sometimes-ambiguous instructions don't help.
Another unpleasant factor regarding stickers is the unpredictable quality of the cutting on the sticker sheet itself; some stickers can be left significantly asymmetrical, or with important features of the art left completely off the sticker. The original Snarl takes that to a new level by having an Autobot symbol that is supposed to be placed in the middle of his dinosaur head... which splits in half in order to transform, necessitating owners either place the sticker asymmetrically on the toy, or cut it in half and apply each half themselves.
One complaint about stickers that pops up that is not really inherent to stickers themselves, but still worth noting, is their aesthetic value even when mint. Throughout Generation 1, much of the robot mode sticker detailing took the form of random multicolored "greeblies", with some more perplexing than others. While excessive amounts of tech detailing are not necessarily a bad thing, some find them very incongruous with the simpler, blockier designs of the early toys, especially their rainbow of colors and occasionally odd stylistic choices, such as the reel-to-reel tape details on Generation 1 Hot Spot's crotch. (Admittedly, the sticker featuring 5-inch floppy disk drives on the original Kup toy, a figure of an "old guy" character, is pretty dang funny.) Some fans prefer to omit certain stickers based on looks alone, particularly if leaving a spot bare could make the toy more closely resemble the animation model.
All told, it's little wonder why stickers have largely fallen out of favor with Hasbro and TakaraTomy, as well as most other toymakers... except for a short, unpopular resurgence beginning with the 2016 Titans Return toyline. The larger boxed toys in this line, and its followup Power of the Primes, had pre-applied foil stickers, with many many many many reports of said stickers coming pre-distressed, wrinkled or misaligned in-package, especially in the latter line. Fans were pretty vocal about this, and the next line, Siege, returned to sticking with paint applications for larger toys' deco.
Aftermarket replacements
Aftermarket manufacturers have sprung up that supply reproduction stickers. Some are available that were designed and never used on the original toy; others are original designs supplied as improvements, providing detail not previously found, to help make the toy more screen- or comic-accurate. Still other designs may allow a toy to be repurposed as a different character, made to resemble a real-life vehicle on which its alt mode is based, improve flaws on official figures, or may add a novelty factor.