Bought a Model 15-1 earlier this year and it is stamped U.S. on the left side of the frame beneath the cylinder opening.
It was shipped on May 15, 1962 to United States Air Force, Financial Officer, Warner-Robins Air Base, GA. Records indicate revolver shipped with 4 inch barrel, with ramp front sight, target hammer and trigger, blue finish, and checkered Walnut square butt stocks. Roy states the revolvers in this shipment were marked on the left side of the frame with the U.S. Air Force property marking (U.S.A.F.) There were several contracts for this revolver totaling 3,000 units.
Wonder my gun gun is stamped with U.S. only.
It is legit.