Need To Know The Hallmark | M Looks Like A Bridge

by Keith
(San deigo)

I have a beautiful strand of Natural Pearls with a diamond heart clasp. It is marked 14k with an M stamp that looks like a bridge. It is not the M mikimoto stamp inside a clam. It looks like an M with an arrow or stuck in the center of the M. Mostly it looks like a bridge. Can you please help? Thanks