*G = Star (Alliance) Gold
SK = SAS, TK = Turkish Airlines, A3 = Aegean Airlines, LH = Lufthansa, LX = Swiss
Two letter codes are usually refer to the IATA airline designator for the airline:
https://en.wikipedia.org/wiki/Airlin...ine_designator
Three letter codes usually to airports:
https://en.wikipedia.org/wiki/Intern...n_airport_code
If you are after lounge access and fast track security the SAS program is I think the best option for you.