What is it about these boundary stones?

I'm finding them everywhere!

This one is beside the road near Rossie Farm, on the Auchtermuchty Recreational Cycle Route. This one is unusual in the fact that it tells you what it is and on top is a representation of the boundary of Auchtermuchty Common.

An Ordinance Survey Benchmark symbol has been make at the base of the stone.

The Auchtermuchty Common boundary stone

The Auchtermuchty Common boundary stone - top