If they look like gang-bangers, assume that that is what they are, and put distance between you and them.
The instant that a mob turns violent against any bystander, assume that you are in a situation of deadly danger.
IMO, giving the impression of normalcy is part of the game. I know it is in the *knock out game*
http://stlouis.cbslocal.com/2011/04/22/st-louis-police-knew-about-knock-out-game-problem/