Help identifying a squash blossom necklace

I have (inherited) a squash blossom necklace and earing set that appears to be silver and tourquoise. Family lore has it that my Dad bought for my mother “on the reservation” in Arizona late 1950s or early 1960s. The marks on it is stamped in the back of the big horseshoe piece, which says “O W T”, and then there are scratchings that look like “REX” on one side and then “S M” on the other. One of the earings also has “REX” scratched on back. These scartchings are only visible in certain light and orientation, so was not able to photograph. Can any one help identify the maker, tribe, date, etc.? Thanks so much!

It is probably a traders mark. Can you send us a picture of the necklace? Thanks for sharing.