Previously owned and definitely vintage, possibly antique in age.  Based on the type of Maker's Mark stamped in the back of the brooch and taking the brooch's style and workmanship in the silversmithing and precision shown in the abalone shell inlay, my best guess is that this brooch was made sometime in the 1940s-1950s.  I can go into detail on my rationale for that assumption if you would like me to; just let me know.  The brooch's pin is held closed only by the tension of the pin being bowed (purposely bent) up.  If the new owner wants a more secure closure, a jewelry repair person could replace the clasp with one that locks when closed.

Dimensions:

Length: 2-3/8 Inches

Width (Bottom to Top): 3/4 Inch

Thickness (with pin closed): 1/2 Inch