I had a little look for this stone this morning as I was passing close by.
The only standing stone I could see in the area was about 0.5m high with the letter S on one side and maybe a letter P on the other. It looked like just a boundary stone to me and not that old but could be wrong. I put a photo here

http://imageshack.us/photo/my-images/338/img4859t.jpg/