First of all, the station's callword was POST GOAL, not POSTAL -- don't expect the poor sap at Offutt to get it right!
Secondly, understand that while some callwords/callsigns are just to provide a simple identifier to be used with ATC and/or mission radio nets & thus used over a long timespan (for example, the REACH # callsigns used by aircraft on Air Mobility Command missions) & often based on a linkable characteristic of the platform ("OLD SALT" being the USS NIMITZ) or related to the history of the unit/mission (many dating back to the Vietnam War), other callsign/callwords are somewhat randomly picked, used for a brief period of time, and sometimes only on one radio net, for operational security reasons. POST GOAL would fall into the latter category.
Some educated guesses can be made, based on the station using that sort of tactical callword, and having ANDVT capability, but they'd still be guesses.
