NATO reporting names.
Yep. Same source of missiles like Grail or Scud.
http://en.wikipedia.org/wiki/NATO_reporting_name#Missiles
Missiles
The initial letter of the name indicated the use of that equipment.
A — air-to-air missiles, example AA-2 Atoll: List of NATO reporting names for air-to-air missiles
K — air-to-surface missiles (from the Russian Kh designation), example AS-17 Krypton: List of NATO reporting names for air-to-surface missiles
G — surface-to-air missiles, SAM (or Ground-to-air), including ship- and submarine-launched, example SA-2 Guideline: List of NATO reporting names for surface-to-air missiles
S — surface-to-surface missiles, including ship- and submarine-launched. (most famously the SS-1 Scud): List of NATO reporting names for surface-to-surface missiles