Navajo Buckle with Hallmarks DD and JA, any help?

I have a silver belt buckle that my husband’s father was given in the 1980’s. It has a beautiful turquoise stone and I believe it may be Navajo. I’m confused by the piece, however, because on the back it has two initials, “DD” and “JA” below it. Does anyone know what the two initials mean? Are there two artisans, perhaps the piece was made at a certain place? Any information or help would be greatly appreciated! I’m very new to this and would like to place a value to the buckle. It hasn’t been cleaned or touched in 30 plus years. Thank you for any help!

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