I had wondered about the bullaun idea, but as there's seemingly none in this part of the Britain (even less than CRs), I opted for the cup-marking option. It seems "safer"! There's also the possibility of it being a Cressett Stone, into which hot wax was poured & candles were lit. This seems to been a decidely christian thing, though I know little more about it. Without additional folklore or history records I don't quite know what we can do with this one....