www.925-1000.com

Oops! I added new information by editing my original post, rather than putting it here.

Please read my original post, which contains the new information.
Thank you!

Thanks for responding, Tom.
Unfortunately, I can't describe the mark any better than the image appears! When I first looked at it, it seemed to be the shape of something, like a chicken or a strange-looking bust of a person -- something with a small head, anyway...
As I looked more closely, I ...

Here is a vermeil brooch that came from my mother-in-law's estate. She was born 1927. The brooch may have belonged to her own mother or another relative before her.

Since my original posting, I have been able to examine the mark under greater magnification, and have been able to find a mark like it ...