Hi and Welcome to Pearl-Guide.
From the looks of your pearls, I would guess they are natural color cultured freshwater pearls from China. I can see the clasp is stamped 4K. Is there a 1 in front of the 4? If so, it would mean 14k gold, or 58.50 parts pure gold. We always like to see the whole clasp and the whole necklace. I also see the other stamped in design, which I would describe as 3 columns. That could be the logo of the manufacturer of the clasp. It is possible the spacer beads are 14K, but a jeweler would have to test them for you.
If you were thinking that is a fancy M for Mikimoto, I can say with authority it is not.
We appreciate any information you have about the necklace, such as its length, history, anything you were told about it, how it was obtained~that sort of info. More photos of the strand and clasp would be appreciated. Thanks!