You know, near most sunset residencies around here there is a bus stop where eldery people go to take a bus "back home". But that bus stop is a fake, no bus stops there. Several times a day someone from the staff walks over to collect the ones sitting there.
Maybe this stone is the same thing? It is close to a then important military installation. Maybe every other day a patrol would come around checking for spies sitting there, brooding and trying to make sense of this. You would need an awful lot of context information to verify or falsify this. But it would be something I would do.
In the end, an interesting question.