I don't believe that it can be welders oxygen. *It can't even be
medical oxygen. *It must be "Gaseous aviator’s breathing" (AVB)
oxygen. *I read it has to do with the moisture content to prevent
freezing. *True?

False. The only oxygen available is just pure oxygen. There are no
classes, categories or separate "paper trails".

I have been told the familiar blue "Aviators Oxygen" oval sticker is
applied at the retail level solely for the purpose of setting a higher
price. There are no government regulations requiring it's use.

It there an FAA regulation on this? *I can't find it.

There are no FAR's addressing oxygen composition. The words "aviation
or aviators oxygen" do not appear in the FAR's nor in any other
regulation I can find. The FAR's only describe when and where
'oxygen' is to be used.