Funny thing is I posted this before going through the pics and actually seeing the Chaos symbol. I was referring to some of the generally scary looking helmets.
As to the SCA and the symbol - it is banned for use in anyone\'s arms because it is a real world symbol easily recognizable, same reason you couldn\'t put a stop sign or the Apple logo.
However, this is Pennsic, and SCA is not the only participant. Most of the guys with horsehair on their helmets are probably not SCA but rather Tuchuks.
Tuchuks do similar stuff but based on fantasy books (Gor). They use SCA fighting rules so traditionally have been allowed at Pennsic. That guy with the Chaos symbol is probably not SCA, or if he is he\'s just ignoring the rules and no one\'s stopped him.