Thanks Jason! During my research I found the following:
“William Singer, the brother of Charlie, Jackie and the late Tommy Singer, has used
various hallmarks since 1972: SD (both side by side and offset), SDX, SDXX, SDV, S/D, all variations of the Singer-Dodge family shop hallmark.
The Singer family grew up in the community of Dilcon on the Navajo Reservation
in Arizona. They have been involved in silver smithing, stone and bead work for quite some time, handing down the skills and artistic ability from one generation to another.” quote taken from an ebay listing description.
I will take the advice to contact Indian Jewelry Supply and will post any info I obtain. Again, thanks for sharing your knowledge much appreciated. TU!