gang as in gangbangers? in USA the gangbangers often have scarves around their head (more often than not, shaved heads) and over sized clothes. This goes for the two big primary gangs that are made up by black people and latinos. Then we have wiggers that dresses the same but their posture and attitude is ridiculous ;pdon't forget the butt that is hanging out from the pants, only just covered up by their boxers.
Oh yeah! I've seen the butt-trick here in the UK too. Very.. err. Glamorous. The gang being sketched out here is UK based and quite 'varied'. Not sure I can say more than that. :D