Agreed, OS = Austrian!
If we're gonna use abbreviations, for simplicity's sake and to avoid ambiguity, why not use the recognized ones? Especially where the "unofficial" version means something else entirely!
Although the thread context demonstrates it's not Austrian Airlines, whilst reading these posts I still find myself having to do a mental double-take whenever I see "OS" - before remembering, "oh, what they MEAN is Openskies...."!
I always thought this (aviation) stuff entailed making one's intentions clear. Spare a moment for the days when we were all being encouraged to fly to/from MIA - glad to see Manchester International Airport have since dropped that abbreviation!