Check out Charles W. Pate's book, U. S. Handguns of World War II, pages 175-185. Pate talks about the Colt Model N, 25 ACP being acquired by Army Ordnance Department's Springfield Ordnance District. Most of these small guns were obtained new or used from dealers.
The OSS was supplied by Army Ordnance and Ser #74631 and #186106 were requested from the Treasury Dept. (along with Ser #129044). The OSS had a hold-up shoulder holster that fired when the wearer's arms were raised (pics on p179).
Guns were marked "U.S.PROPERTY" and "UNITED STATES PROPERTY" on the right side of the frame above the trigger guard (p180). The author believes the markings were added post-war after the OSS returned them to the army. Pantographed markings are considered fake by the author who believes they were done not to defraud but to enhance them as gifts to friends (p181). Some have been seen with the ordnance escutcheon (Ser #402157, #407667, #407534) (p183).
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!