What is the value of this antique trombone?

I recently came across an antique trombone. It is marked "USMC" and the manufacturer is listed as "C.G. Conn Co, Elkhart, Indiana." I have scoured google and can't find any results for this trombone with the USMC marking which seems to be the unique part of this item. I know the vintage Conn trombones are quite valuable, but am having a hard time coming up with additional information on this one. Any help on further info about this trombone and its potential value would be appreciated. Thanks.