Update: In addition to this rock, there is cross carved in a tree directly behind it. The top bends over a bit. Next to that tree is an imprint of a horseshoe, complete with nail holes. It points in the same direction as the top of the cross. They both point in the same direction as the bottom of the Y's, assuming they aren't pointing down into the ground.
I was just reading a local history account written about 100 years ago. It briefly mentioned that when the closest town was settled, people reopened and worked some old mines in an area that's about 2 miles from me. My markers point right at it. It's all on private property. I haven't found anything that seems related on my property. It didn't say what they were mining or anything about the origins of the mines.
So, I assume this was a trail marker to the nearby mines. I still wonder what v y y means. I know there were some Spanish mines in a neighboring county. I only know the general area of those mines, but this seems like it would be along the way between the 2 areas.