Colonel Frank J. Atwood was the officer in charge of inspection and acceptance for the Rochester Ordnance District from mid 1942 until early in 1946. In addition to Remington Rand and Ithaca 1911A1 pistols, his initials will also be found on Model 1903, 1903-A3, and 1903-A4 rifles made by Remington Arms as well as 1903-A3 rifles made by Smith-Corona. They will also be found on shotguns made by Remington Arms, and M1 Carbines made by National Postal Meter. His initials will even be found on the M6 knife scabbards made for the M3 knife, and binoculars made by Square-D. There are others that escape me at this time, and all the inspections were done by people that worked under his command.
His initials will not be found on anything manufactured by Colt.
FJA inspector marks were on Ithaca and Remington Rand 1911A1 pistols during WWII. Not uncommon for Colt slide to end up on an Ithaca or Remington Rand frame during the many refits most of them went through.