The gun has been poorly refinished

[Linked Image from photos.smugmug.com]

The 'case colors' on the sideplates and action are from heating the metal with a torch and using cold blue to produce colors

[Linked Image from photos.smugmug.com]

The barrels, triggers and trigger guard have been blued, likely with hot caustic salts meaning the 2 barrels and ribs will, before long, separate.
The barrels are damascus and it is likely they were cut. A gunsmith could measure the length of the choke constriction to confirm, and you might see a gap between the keels and barrels at the muzzle.

[Linked Image from photos.smugmug.com]

We think 'SD&G' is Schoverling, Dales & Gales; a large sporting goods firm in New York City.

If you can return the gun, do it.