Rubsign
A rubsign was a small heat-sensitive sticker that came pre-applied to Generation 1 toys beginning in the line's second year, 1985. They would reveal an Autobot or Decepticon symbol upon being rubbed. The Mini Spies were the first toys to feature rubsigns. The purpose of the rubsign addition was to help consumers distinguish genuine Transformers toys from the many knockoffs their success inspired (off-brand versions of the Dinobots, Soundwave, and his cassettes were particularly common in 84/85), as well as the Tonka Go-Bots and other competitors.
Operating principles
Demons make the color change. Anybody who tells you different is a witch, and should be burned, burned at the stake. Death to the evildoers!
Ahem. The working part of a rubsign is a layer of Mylar plastic which contains thermochromic liquid crystals. At different temperatures, the liquid crystals' molecular structure changes, reflecting different wavelengths of light, and making a visible faction symbol appear. Mood rings work by the same principle, but have more bogus magical properties.
