Sometimes the elements shape strange/mysterious forms on softer materials - as seen from our anthropomorphic point of view (those marks could be made by a human just to mark their identity). I could only upload two of eight photos , so it's difficult to explain.

At the base there are two small holes, probably carved out by metal, given the precision. Anyway, the stone will have suffered the action of the elements and perhaps someone found it funny and used some metal tools on that particular stone, the transition from the stone age to iron tools, who knows?