A tampograph is a printed graphic image produced by a specific printing process called tampography.
Tampography, also called pad printing or sometimes tampo printing, combines rubber stamping and offset printing. The desired image is etched into a metal plate. This plate, also known as a cliché, has the image lines sunken into its surface. They are said to be in negative relief. Ink is deposited into these lines; the excess wiped away, and then a rubber pad or tampon is pressed against the plate to pick up the image. The pad is then pressed against the surface to be decorated, leaving the image behind.
Because of the precision of the metal plate and the flexibility of the rubber pad, this process can produce very finely detailed images on irregular surfaces. Furthermore, the process is well-suited to mass production. Most graphics on toys such as Transformers --such as multi-colored faction symbols-- and die-cast cars are tampographed.
Tampographs replacing stickers
For the original Transformers toys from 1984 and 1985, those details were still added in the form of stickers; but as technologies progressed, stickers would be eventually phased out in favor of tempographed graphics (with the exception being most re-issues of older toys).
The main advantages of tampographs as compared to stickers are that tampographs are always factory-applied, whereas stickers often require the buyer to attach them by hand (which, depending on individual skills, can have less than stellar results); and the fact that, assuming good quality control being in place, tampographs wear off less easily than stickers.