No ct mark but anchor and letter M -need help!

by Stacey
(Narberth, PA USA)

I recently bought this ring and didn't see the hallmarks until I got home. It was sold to me as a 1920's 14 ct ring. However, it tests 18 ct and has these stamps, none of which appear to be quality/ct stamps. The anchor would indicate Birmingham, but when I look up the letter "M" in the assay office none look like this. Help is appreciated to help me make sense of this!

Thanks,

Stacey