Metallica is always a cool theme for anything. Tattoos, black t-shirts, bumper stickers, birthday cakes, whatever. My personal favorite metallic logo was the "metal up your ass" shirt of the late 80's. When I was in high school wearing that shirt meant instant detention.
When I am not carving pumpkins, I run a bulletproof vest company. BulletSafe Bulletproof Vests are the value leader in body armor. We are very popular with people like armored car operators and ATM repairmen.