A couple examples of USMC pistols belts use in the early years and prior to WWII. These USMC contracted belts do not have the U.S. stamp on the exterior.
Collectors need to exercise extreme caution when buying these belts as most are fakes made out of surplus non-U.S. marked belts intended for lend-lease.
Hopefully these photo will give a feel for what original USMC stamped belts look like:
This only known period photo I know of that actually shows the USMC stamp: