Mikimoto pearl jewelry always has a small symbol of an oyster stamped on the metal pieces. The name may also be engraved on the piece.
Mikimoto's trademark resembles the outline of an oyster. Mikimoto places their maker's mark on the clasp of any necklaces and bracelets they create. They also add a small charm with a tiny "M" on them. The mark can be found inside any ring made with their pearls. Mikimoto earrings and brooches will have the mark on the back of the jewelry. A Mikimoto store or a retailer who sells Mikimoto can verify authenticity and give an appraisal on the jewelry.