Three of the Following Teenagers May Very Well Be Members

Three of the following teenagers may very well be members of a gang. Which one is least likely to be a gang member?

A) Mort greets certain peers in the school corridors with odd hand signals.
B) Randall has just gotten a strange symbol tattooed on the outside of his left wrist.
C) Jason suddenly withdraws from old friends and spends his evenings alone in his room.
D) Sean and his buddies delight in spray-painting graffiti on buildings in certain neighborhoods.