I've had a Selmer HS* crystal mouthpiece for about twenty five years. I picked it up at dear old Hunleth Music, on Broadway in downtown Saint Louis, spending all of about fifteen bucks for it at the time.
It was "signed" and the facing code applied to the bark end of the table with some sort of engraving tool. No other markings other than that.
While I like the tone that I get with the mouthpiece, one thing about it that I could not stand was the "sizzle" that was very audible to me (although inaudible to anyone else). The problem does not occur with other (rubber) HS* mouthpieces that appear to be identical (at least in chamber volume, checked by comparing the amount of water that fits in the plugged up chamber.).
This, plus the teeth on the glass problem that most have with these "crystal" mouthpieces, relegated the otherwise wonderful mouthpiece to the "big box of mouthpieces" that resides in the music room closet. A shame, but what are you going to do?