It is either a Remington Rand or Ithaca frame with a Union switch slide on it. RR or Ithaca depends on serial number. FJA was for either RR or Ithaca, if it was a US&S frame it would have RCD inside a circle in the same spot. Still a nice acquisition with CMP provenance.
Serial is 203xxxx so it seems to be a Remington Rand frame from 1944.
[EDIT] ok - I get it now. CMP put a tag on the pistol and it has the make of the slide and the make of the frame;
S - US&S (slide Union Switch & Signal)
F - RR (frame Remington Rand)
I'm a little slow