Copyright infringement is very difficult to prove - the infringement must match the copyrighted product EXACTLY.
I do want to say that I am a HUGE fan or Eric. However, I am also a US Marine. The skull (with or without the crossed rifles) has long been a graphic/symbol used on Marine Corps stuff. Hell, I have a tattoo on my arm from 2005 that looks almost identical to the skull on one of the shirts that was sold on eric's website. It also looks identical to the drum set they were using on tour a year or two ago. Huge fan or Eric, but come on, let the Marines have their damn hoodies lol.