Hey- From experience (painful): Mark the number on the outside of the trigger guard in clearly visible ink (paint a white acrylic patch on top of the B-72 and then write the number in black if the metal finish is dark.) Our collection areas and exhibit areas are not well lit (well, they're not suppose to be, are they?) and trying to squint at a number skillfully hidden on the inside of a trigger guard leads to a lot of flipping of said longarm leading to accidents like hitting the cabinet next to you or something on the table. Alright, maybe not if it's on exhibit.... Also, about the comment of reversibility and thieves: Unless you have skillfully written your museum's name on the gun, the catalog number is not going to mean much to thieves or buyers. We have a collection where the donor painted numbers on the stocks on messy white splotches of paint (pretty much irreversible.) I would suspect that guns in circulation would have a lot of such marks--your museum's mark would not draw comment so it is not a security feature in that sense. It is a security feature in keeping it identified--without it's number and attached records, in a hundred years when we're all dead and gone would a new worker still identify the longarm as Napoleon's gun? (Unless his name is engraved on the stock like our Sam Houston pistol and Mirabeau Lamar shotgun...Texas guys....) Collections care includes control of information. Sally Baulch Collections Manager, Anthropology/History Texas Memorial Museum PS: Since you're asking about renumbering guns, you ought to ask how to number the horn chairs on exhibit :)