Without being able to wear your gang colors the only way to identify a member is with tattoos. A tattoo gun is made by hooking up a walkman motor to a pen casing with a guitar string for a needle. The ink is made by burning black chess pieces. It is forbidden to do tattoos but the motors are quiet enough that a guest in your cell can get a good few hours of work done without getting caught. Just tell the porter to leave your cell open so you can clean it and, after the guard has made his rounds, your tattoo shop is open for business.