Prior to the U.S. entry into WWII , our law made it illegal to export help to foreign wars. This change on Dec 7th 1941 when we declared war on Japan, and on Dec 11 when Germany declared war on us ( no one really knows why Hitler decided to do so. they can only guess , even his staff were caught by surprised ). Prior to these dates FDR got around the law by " Lending or Leasing " war material. Because we were only loaning equipment it had to be marked " Property of the US ". Once we actively were engaged in hostilities this marking was no longer necessary and the markings were dropped as a unneeded step in production. I don't have a book handy but those who are better versed in the history of the Enfield can confirm it, but I believe it was in 1943 when the markings were dropped. could be wrong, been wrong before and I'm pretty sure I might be wrong again in the future
