After doing some research online, that appears to be what was known as a Martin "Stencil" horn. Not an official "Martin" I guess as they say, but made by Martin. It's hard to tell from the picture the size, but it "looks" like it may be a C-melody horn - made around the '20s - '30s but not really used any longer as a normal keyed sax. Or it may be a tenor but it just looks a little smaller to me for some reason in your pic, which would tell me C-melody. It's not worth a mint or anything, but a nice old horn. There are collectors for Martins out there that dig old horns like that.