And Further Why it was originally chosen: (from the article above) Chris Kyle explained his use of the skull best in his autobiography, American Sniper: “Our Comms guy suggested it before the deployment. We all thought what the Punisher did was cool: He righted wrongs. He killed bad guys. He made wrongdoers fear him. That’s what we were all about. So we adapted his symbol  — a skull — and made it our own, with some modifications. We spray-painted it on our Hummers and body armor, and our helmets and all our guns. And we spray-painted it on every building or wall we could. We wanted people to know, we’re here and we want to f*ck with you… It was our version of PsyOps. You see us? We’re the people kicking your ass. Fear us. Because we will kill you, mother f*cker. You are bad — we are badder.