http://www.textfiles.com/fun/armstech.txt
Has entries for all the US carriers (towards the bottom) amongst other vessels worldwide..
Only the large navy US has the F/S tag, and it can have the following values (at least)
AA
PA
Bldg
SLEP
SLEP/AA
Which suggests F/S stands for Fleet Status or similar - Fleet Service?.
AA ~ Atlantic Area (ie east coast)
PA ~ Pacific Area (ie west coast)
Bldg = Under construction.
SLEP = Service Life Enhancement Programme