i was at a shoot one time, a few of us around the fire, one of the gents picked up a pc of thin metal from somewhere and just out of the blue started heating it and burning a pattern into the top of a stump. every now and then he would put a different bend in the metal and keep adding to his design. it all looked like a spur of the moment creative whim to me. by the time the evening was over he had created was a real nice bit of artwork. so i would guess burnt in designs were created centuries ago aswell, but probably not too often on personal guns if at all., military may have branded ID marks into their guns, i don't know.
ou
tom