Vintage Navajo Pendant with Kingman Nugget

I've collected Native American jewelry since the early 70's. My Mom got me started on it as a kid with trinkets, mainly because that's what she did as a kid. She is also part Mississippi Choctaw/ Chickasaw/Cherokee so is a bit of a fan

This pendant, has a rather crude bezel but I do love it. It's not often one sees an older piece of Kingman turquoise anymore and I still like nuggets. I have been stumped by the hallmark forever and have never found it. It's probably a now defunct trading post. It measures 1-1/2" x 3/4" and is marked sterling.

Thanks for looking. If anybody has info on this hallmark, I would appreciate your input. I've exhausted my resources, in addition to the resources of quite a few galleries.