ETA: It turned out to be a bunch of bored and procrastinating grad students in Penn's urban studies program. Most overeducated vigil ever! Which turned into a bit of a riot after we started stealing all the wawa signage. And apparently I just missed the TV cameras. Shame. There were really fun signs, though. Pictures on request, if they turned out fine from my cameraphone. (I really need a real camera.)
ETA 2: More info.