It's a gangsta sign
Gangs in New Yoik & LA 'throw' their signs like that - it's a way to identify each other in the street and can be done quite subtley.
Chavs think they are gangastaz if they do an approximation of this.
(
Je suis un vagabond is an unfunny, up your own arse middle class knob,
Thu 17 Jul 2008, 17:09,
archived)