Dad passed away and I found this while cleaning out garage. Any help would be appreciated. Is it a gas cap/ horn button/ trunk ornament/ etc. Thank you in advance for any help you can give.

 

Can you put a picture of the back? I need to see how (and thus what) what it attaches to. I am a Falcon driver and a Fairlane owner, but I act like I own the Falcon (cocky grandson that I am.) Horn buttons should have three plastic hook-like things, wedges is a more accurate description, but Gas caps should have two small ***** sticking out so that it pressurizes when turned. Otherwise I don't remember any ornamentation looking like that, possibly a hub-cap ornament for a later model? Check out some Mustang wheels & you'll see what I'm talking about.