Mikimoto pendant

[Winehouse]

I have a mikimoto pendant my father bought for my mother in the 50s. It is stamped M on the chain & pendant but I can’t find any metal stamps. Does anyone know why mikimoto wouldn’t have put a metal stamp on this? Thanks in advance

 

[CortezPearls]

The "M" stamp does look like Mikimoto's, but it sure is odd not to see the metal stamped somewhere on the item.
Never seen a pendant like this one before, and the pearl does look like a Mikimoto.

 

[Winehouse]

Thank you for your response! You helped me a lot.