[WhizzbangK.C.]

Come to think of it all of STD stuff had their logo on it, they were proud of their better product (not making barely OEM replacement parts).....

The specific font of the numbers on the STD and the OP's match though, and it doesn't look like a commonly available commercial stamp. If you look at the OP's case, you can see straight lines going vertically over the numbers, looks like file or course sand paper marks instead of rough cast. Possibly a previous owner or the builder removed the STD logo and carefully blended the area.