How the Hack Changes Tattoos

My favorite Philip K. Dick book is a scanner darkly, which is about a policeman who is in the drug squad and is hired to hunt down himself. There's a drug that people are taking that causes schizophrenic reactions. It's very cool. Kind of grungy southern California version of cyberpunk. I want to know before we figure out how the hack changes that tattoos. What do the tattoos do when they're working properly? Is it just a connectivity thing? And do they cue as cool as your wow character?