CMP 1911: Marine Corps pistol?

So my lottery number came up and the CMP sent me this Colt Field Grade. Looks to have a O-68 etched below the serial number (see last photo). Possible Marine Corps rebuild?

https://www.milsurps.com/images/impo.../qpqCeJq-1.jpg
https://www.milsurps.com/images/impo.../fsUogy1-1.jpg
https://www.milsurps.com/images/impo...VUvBjpg1-1.jpg
https://www.milsurps.com/images/impo...41MVjpg1-1.jpg

thanks
Jon

I have seen garands marked that way. Ogden depot rebuilds.

+1 they are marked behind the rear sight that way on Garands and are scarce. Nice catch on a nice 1911......

Thanks. Accurate as well after taking it to the range