Is that the boundary wall for Gwrych Castle that runs between Llanddulas and Abergele. Blowing up the pic to try and read it, not clear, but I think the right hand side says Llanddulas, Conway, Bangor and ? ... the left hand side I think says Abergele, ?, Chester, London (?) ... so is it a sort of milestone although I cannot see any mileages! Presumably a boundary marker between properties or perhaps parishes.
Or I could be on completely the wrong track!!!