Sorry if this has been mentioned before..
Nitrox cleaned and O2 cleaned are two different things.
For some shops they could be the same, but generally 'Nitrox ready/clean/compatible' are up to (MAX) 40% O2 content
They might not use O2 compatible lube, o rings or check thoroughly while cleaning valves.... So NO PP blending!
**this now has become a check with me when I get my tanks inspected, I drain them, crack off the valve and inspect the tank quickly and the I ring, then get it filled .... Had a few shops "O2 clean" tanks that had surface rust and wrong O rings when I pulled then apart to change out valves on the first fill**
As for tank wrappers, as an individual owner of personal tanks, whatever you want. As long as you have something to show for that the tank/valve has been cleaned for Nitrox or O2 and a current analysis of what is in the tank(s).
As for a commercial operation with a 'fleet' of tanks for rent/charter, then some sort of marking system should be in place (painted or wrapped tanks).
Same thing with dive boats where tanks are provided (ie Caribbean). No one might know if anything other than air is in a clean AL80, but that one that is a different colour, or has a band on it, might contain something other than Air (including He).
Joe Random isn't going to be renting your personal tanks, so there is little worry about what kind of marker to show what is in them (to Joe Random), but if you provide a service of renting tanks with Air, Nitrox and He, you better well have a system in place, otherwise no one would know what is what with no markings (staff and customers).
My tanks have up to 4 stickers/markings on them (only deco bottles with MOD)
1 - Vis sticker with o2 clean on bottom/inside (doubles)
2 - My initials (lower outside)
3 - MOD (21m, 6m) (higher outside)
4 - Daily analysis tape (neck)
And for sake of thoroughness, my drysuit inflate has a warning sticker (and Vis) saying that there is most likely anything but air inside the AL6, and you will die if you try to breath it.
BRad