A huge gang of (what I presume are) Comic-Con International attendees, wandering the streets of San Diego in Joker face paint.
You won’t see a group of cowl-clad Batmen following them. It’s too damn hot here in San Diego for cowls. It’s just not cowl weather.
UPDATE: This is apparently part of a viral marketing campaign for The Dark Knight. Well done, marketers. Consider it, um… virused.