Brent, it could mean either... "New Old Stock" or "Nitrous Oxide Systems." "N.O.S." is correct - but you can't really see it in that picture. The blue bottle is their signature style, I think - but I think that some sort of color coding is mandatory on all bottled gases (oxygen is green, for example).

They also put in additives so that you can't run the foggers INSIDE the passenger compartment.