Ha! I was going to say “what it wouldn’t fit in your vice” but somebody beat me to it.
In this case stamps are the answer not only for ease of application but because the work hardened impression can be seen with acid even if thieves sand it off. This technique has been used by state police forever to catch people re-stamping stolen harley davidson motorcycles which was a popular vice for the outlaw set back before every part on the bike had serial numbers to confound chop shops.