Vintage Sterling Silver 1940's Black Onyx Signet Ring

A vintage sterling silver signet ring set with an oval black onyx cabochon and a faceted glass rhinestone in the center. The back of the setting is open and the band is marked sterling with a maker's mark I can't quite make out. I believe it was likely made sometime during the 1940's. 

Black onyx is a protection stone and is believed to promote strength during difficult times.

Size 9.

Condition: Some surface scuffing to the band and one light scratch mark to the onyx. A little bit of residue on the back of the stone that is stubborn to clean off.