Vintage Mother of Pearl Heart Earrings Sterling? Boho

Vintage mother of pearl heart earrings. There is a stamp on the back of the heart, but I can not make it out at all, even with a jeweler's loupe. It is not legible.

I tried to show the back in the last photo. They polish like sterling. But I can't say for sure that they are sterling. they may be alpaca.

They measure 4 1/2" long from the top of the ear wire to the middle center longest part. Excellent shape!