I think Leviton can inscribe whatever you want on their wall plates....probably if you order them in lots of a million or so...who knows.
I've seen some wall switches in certain enclosed copy rooms at work with the word "FAN" printed directly on the rocker in bold black letters. These are connected to exhaust fans...I guess to suck out all the ozone fumes from huge copiers, laser printers, etc. going all at once.
But to me it seems outrageous to pay $6 for what is essentially a piece of plastic with what seems to be mass-produced lettering.
On the other hand...it sure beats those little stickers....