Could the OP determine he was a gang banger? Yes, having been around many gang bangers myself, I know that one can intelligently estimate whether someone is a gang banger or not.
...however, many youngsters dress the part, yet these same youths are not actually thugs or gang-bangers. Not even remotely. So "estimations" are just that...guesses.
In my experience, certain tattoos are more indicative of gang affiliation than are clothes...or shooting styles.