Baggs you have answered a puzzle for me. We have one of those marks on the wall next to our gate post, I wondered what it was. We get a lot of walkers passing by in the summer but I haven't noticed anyone studying it, but it is a bit worn and indistinct.
I like finding a tropograph on a high point. It helps me understand the topography better as I gaze out. I remember seeing one in Wales that was etched onto a long brass plate. The etcher had made a beautiful scene with exquisite lettering.
As Nannagarra says they are toposcopes or topographs. They are placed on high land and show all the places you can see from that point. Triangulation points, usually a stone pillar, set on a hill top are not the same thing. It was originally, a very British innovation for measuring distances and positions from one point to another. They are now longer used as we have GPS etc.
We bought an old house in a quiet village, we couldn’t understand why every weekend people would pull up outside in their cars and then get out and start hunting around our boundary.
Eventually we asked, it turned out a pub in the next village ran treasure hunts, the trig point on our wall was one of the clues.
I just can't think what those normally brass/bronze plaques that are on high points on hillsides. They give you the distances of various points that can be seen. Thanking you in advance