This semester the local school I am going to has a course that is a pilot program for another course in security threat groups. One of the texts we use is this one. There is another text that covers tattoos.
http://www.amazon.com/Gang-Intellige.../dp/0873648447
The other text we use is:
http://www.amazon.com/Gangs-Guide-Un.../dp/1563250780
Pretty interesting stuff.
get you started.