Unless the serial number of the gun the OP is referring to is listed in NCIC as stolen property, I would not worry about it. Many US military pistols and rifles have been sold as surplus over the years and are in civilian hands. There are a few on this forum that have posted photos of their USAF marked S&W Mod 15's as well as other guns. The OP can contact his local law enforcement agency and have them run the serial number, which would not be a bad idea..