This kind of carving it's very ancient. It's called Y or "phi" engraves or crossbow-shape engrave. It's a stylized abstraction of human body.
It's a cruciform and reminds christian crosses. But was made before Christianity.
Those carvings are wide-spread in most of the rocks in the sites of Mount Beigua's Park area often side by side with real christian crosses made by monks to "exorcise" the sites.