Tattoos of the roman soldiers

First, we have to say that the tattoos, called "stigmata" in Latin, were not good considered from wealthy and important roman citizens. In fact, tattoos were a characteristic of the barbarians. The only kind of roman citizens, not born as barbarian, that had tattoos was the soldier.
These soldiers were used to get tattooed "SPQR", the name of their legion, the symbol of their legion (see the post Military symbols ) or the name of their general officer. In the imperial age soldiers were used to get tattooed also the name of the Emperor.

Bibliography:

"Tatuaggio; dalle origini ai giorni d'oggi" di Andrea Palmeri