What does a bullet necklace symbolize?

Starting, I believe, with Marine Corps Scout Snipers and moving to other places in the military -- and eventually beyond. The general idea is that, everyone has a bullet with their name on it somewhere -- that is to say the instrument of their own mortality. A bullet necklace is a charm. It is meant to symbolize THE bullet that is destined to kill you. Since the wearer possess their own ghost maker, it is not out their waiting to hit you and you are, if the superstition is taken literally, immortal.

I suspect that, as with most symbols and charms, people usually just wear them because they think they are cool.