If you've picked up brass that someone else has shot, then their gun's marks will be on the rounds that you reload and shoot.
Oh goody, yet another excuse to send ninjas into innocent people's homes at 2 am.
Until you deprime the case. The mark (of the beast?) seems to be put on the fireing pin, which transfers it to the primer. As someone else pointed out. A polished firing pin, or a new one, will fix the problem. Put in a fireing pin from some other gun, or one you got at the show for a "spare", do the deed, and return the original firing pin to the gun. Of course crooks aren't that smart or patient. They just steal the gun, or buy a stolen one, then do the deed, then throw the gun away, or sell it to someone dumber than they are, well the less dumb ones do.
This is a solution to the wrong problem. The gun doesn't commit the crime, the shooter does. This is even worse than stoplight cameras, since at least some of those show who was driving, this