Yep scary.
What better way to train as an urban warrior than in the Army.
I suspect that most of these gang members are not serving in combat arms MOS's, and especially not in the infantry where they would really develop urban fighting skills. Most likely they are serving in supply or support positions. The gang bangers are just there for the money or access to goodies, and don't see any reason to die for "The Man."
That doesn't mean they won't come away from their service without having learned anything. But they won't be experienced urban tacticians, either.
I would also guess that a lot of this graffitti isn't coming from gang members. Just like in some of our own cities, a lot of this stuff probably comes from bored kids from the suburbs trying to emulate the hip-hop culture they adore.