Anvil Arms is a local company to me and they do a pretty kick butt job of laser engraving firearms, generally AR lowers. Check out their gallery here.
For $15 (and since I can drop it off and avoid shipping fees), I am seeeeeriously thinking about doing something to mine. I can't erase the Bushmaster .223 / 5.56 markings, but on the other side I definitely could have some fun.
I was thinking something like a warning (similar to this one) that says
CAUTION: Proper use of this product may induce PSH in certain individuals.
I'd love to hear your ideas. Heck, it might even be some sort of contest to let someone "Pimp my EBR" or something ;)