Welcome to the forum, @TawnyElam. What a great thrifting find!
To me, your concho belt does resemble deeply stamped and/or chiseled overlay Navajo work. Similar design characteristics and aesthetics have been used by famed Navajo silversmiths Emerson Bill and his nephew Darin Bill (1965-2003), for example. Your belt looks to be hand stamped, with diamond appliqués soldered on, to me.
https://www.bischoffsgallery.com/online-store/jewelry/silversmith-lapidary-biographies/wilson-begay-2786.htm
Belt buckle by Darin Bill
I can’t help with identifying the artist or providing clarification as to the hallmark, but I do have some thoughts.
I agree with Zia that it’s anybody’s guess. Also, considering it’s a relatively common practice to conjoin letters in this manner for a hallmark, (bear with me here, guys) it may not even be the same artist that crafted Zia’s beautiful, drop dead gorgeous cuff. At the very least, it’s a possibility that shouldn’t be discounted, I feel.
I have worked with Medicine Man a number of times, and can’t say enough great things about the establishment. However, to throw a big wrench in the mix, while Medicine Man is a renowned gallery and it’s proprietor, Mark Sublette, is highly regarded, everyone makes honest mistakes. A concho belt sold in one of their auctions last year that was no doubt a Skeet creation, evidenced by the buckle: the design and overall execution of which is unmistakable. It was listed as being crafted by Roger Skeet Sr., but the buckle is clearly marked with Roger Skeet Jr.’s hallmark. Roger Skeet Sr. made countless pieces for C.G. Wallace and did not hallmark his work.
https://www.auctionmedicinemangallery.com/auction-lot/roger-skeet-sr.-navajo-second-phase-revival_f20499d85e
I only wanted to bring that up so tunnel vision doesn’t settle in. I think it’s important to keep an open mind, especially with things like this. But hey, that’s just me. 
Congrats again, @TawnyElam on a lovely belt. If you get around to wearing it, perhaps you wouldn’t mind sharing it in @Ziacat’s thread, How do we combine and wear our Native American bling . 