Agree.
Only they can hammer punches deep into the tank neck.
Actually anyone can stamp the CROWN of a cylinder (in the U.S. I don't know what the laws are in other countries.) (except for composite cylinders of course which aren't stamped at all.)
Stamping the sidewall condemns the tank (US DOT/UN-ISO..."condemn all sidewall stamped US DOT and UN-ISO cylinders".
The issue comes when you get ready to sell the tank. The new owner might not like your initials stamped in the crown of "his" new tank and he can't legally remove the mark without condemning the tank.
Had a dive buddy who stamped his initials into his tank "HLN". All fine and dandy. He sold the tank to another dive buddy who promptly stamped out the initials. That condemns the cylinder. Even if the cylinder would otherwise pass a VIP.
So you might choose something less "permanent" unless you plan to keep the tank until the end of it's service life.
49 CFR..."All markings must be legible and unblemished."
The exception is if you try to "forge" something that isn't supposed to be there, like adding a "+" or altering the working pressure or serial number or adding your own hydro mark. Had a guy bring in a cylinder for VIP last year and the RIN mark looked suspicious. The letters in the RIN stamp were not all the same size and some were crooked, like they were stamped one at a time and not stamped with a single die like a hydro tester uses. I called the hydro facility indicated by the hydro mark and he looked up the serial# in his logbook and said the cylinder had never been in his possession. The cylinder was condemned.
Also had a guy a couple years ago bring an aluminum cylinder in for VIP and he had added a "+" onto the hydro RIN stamp. Cylinder was condemned. (US DOT..."No aluminum tanks qualify for a "+" stamp and any aluminum cylinder bearing a "+" mark must be removed from service")
DOT says if a hydro inspector makes an error in his hydro mark, it condemns the cylinder if the makes the error illegible. The prescribed way for him to correct his error is to stamp the correct marking above his error stamp. (US DOT..."When a hydro tester makes an error in marking a cylinder, DO NOT have the hydro tester mark out the error. Stamp the correct marking above the error."
I believe the reasoning behind this is that marking you stamped out that you claim said "Fred's Tank" might have actually said "Condemned".
Once it's there, it has to stay there and be "legible and unblemished" according to US DOT and UN-ISO.