Trying to identify a hallmark

I found a turquoise and silver bolo in a box of jewelry from my grandmother, it measures 2"x 2-1/2" with 13 pieces of turquoise on it.
There is a hallmark etched (not stamped) on the back. OMXZ with a + sign underneath.
There is rope detailing, braided leather tie and silver tips.
Can anyone identify the maker, and help me determine its value?

Hello, if you could please add a picture of the workmanship and mark. Thank you.

Sorry for the delay in replying, here are some photos.
Scratched on th back is OMXZ with a + under it

Hello, thanks for the image. That is not a hallmark. A dealer will use that to tell him how much cost he has in an item.

Thank you.
So it’s something to show how much its worth?
I am just trying to determine a fair price for it, would you have any idea what it’s worth?

We have similar pieces that are new that sell for $140.