Nothing, other than, like the more numerous DSC contract guns, they are lacking the US property markings on the top strap. Only a letter can reveal whether you have one or the other.

As for the USMC markings Ron asked about, Pate notes them as “possible fakes” (to benefit from the Marine Corps association). I do remember that we had a discussion here some time ago about a USMC-stamped gun that lettered as a DSC contract delivery to a shipyard (the name escapes me), but I recall no definite conclusion. I’m not aware of any matches of USMC-stamped guns lettering to the Maritime Commission.