Proof marks are Spanish, Eibar proofing house, in use from 1931 to present. There should be a date code on it but it looks as though most of the markings on it have been filed off to make it look older than it actually is. There might be more markings on the underside of the barrel or the tang that escaped obliteration. My best guess is it's a modern reproduction derringer imported and sold here several decades ago as a Lincoln Derringer.
If it shoots and the barrel isn't rusted up from a careless owners neglect in cleaning it after playing with it, you might get a hundred bucks in a private sale give or take ten or twenty bucks, less if you sell it to a dealer, they need to make a profit.
If the barrel is still in good condition and you want to make it go bang, find a wedge for the barrel, it will help keep the barrel in the stock under recoil.