There are exclusive pearl jewelry lines distributed by MIKIMOTO. These lines are Blue Lagoon, Gordon's Classic Collection, Sea Magic and Zales Signature Collection for Zales Jewelry. They should not be confused with MIKIMOTO brand pearls.
If the underside of clasp is stamped 18K which is high caratage, Marilyn this is an indication the pearls are high quality. Are the pearls individually knotted? This is another indication of a good quality strand of pearls.
Sorry can't help with the letters RJSA or RISA , a photo of mark would help speed along research. Unfortunately, due to time constraints, I can only devote so much time to each question.
