As Doverham said, the gun has French (St. Etienne) proofmarks. It's pretty unusual to find French-made barrels on anything other than French guns, so I'd be confident in saying that what you have there is a French 16ga. I don't think the silver medal refers to the grade of the specific gun, however, but rather to a medal awarded to the gunmaker in question. Unfortunately, there's no way to tell the make of the gun from the photo you provided. And there might not have been a maker's name on the barrels or action--although the "silver medal" makes it somewhat more likely that the maker would have been identified. No way to estimate value from that photo. Good luck in recovering it.
