I went out with a bit of paint and a wire brush and dressed up the town line stones that I re-discovered.
This one is down by the road, upright and apparently secured by a glob of concrete that does not extend above ground. The B was reasonable\y visible (for Barkhamsted), but the C was completely obscured by lichen growth and needed some wire brushing. I only knew it was there because I could see the B on the other side.
Up the hill heading east up the steep hill toward the N corner of the house. I was not all that confident of finding it, as there is a lot of laurel and deadfall in the area, but it wasn't at all buried. There's a pretty good sized boulder just S of the line between the two-sided stone and the bottom of the clearing below the hot tub, so easy enough to find it again.
This is the one I liberated from the leaves, duff and deadfall the other day, and the one that I generally pass within 25' of most days at least once.