Tattoos are a visual accessory the player can purchase for Jimmy Hopkins.
Tattoos can be purchased from a trailer in Blue Skies Industrial Park, meaning that Jimmy can't get a tattoo until Chapter 5. They don't have much impact on gameplay, but other characters will comment on them. The only cliques with a positive opinion on tattoos are the Bullies, the Greasers and the Townies, other cliques will insult them. Sometimes, prefects will yell at Jimmy for having one.
Once Jimmy has purchased a tattoo, he can't have it removed all together.