ID a hallmark made with a chisel or similar

[azsungal77]

I have searched everywhere for this hallmark. I have not found it anywhere. This ring is part of my mother's collection and she collected for over 30 years that I know of. It is an unusual ring, to me, and a beautiful green turquoise. Any help?
http://i927.photobucket.com/albums/ad118/charlyb777/Indian%20Jewelry/greenringbackandhallmark-1.jpg

[azsungal77]

I thought I should add a pic of the front side. We think it is Navajo, But I can't find who anywhere. Any help would be nice.
http://i927.photobucket.com/albums/ad118/charlyb777/Indian%20Jewelry/greenringfront2.jpg