I can't see one , but that doesn't mean much .
A low sun with water on the markings and pic taken into the light could bring it out if it is there .

I can see exactly what you mean. But I think we're both imagining it?! I can see one round the dent in the lower left of the picture too. And on the other photo all sorts of shapes appear. People who like ghosts see those in photos. I used to see animals in our old carpet. There was a great crocodile in a cloud the other day. But rock art fans see cup and rings. Paradolia if you want a posh word for it.

Or maybe it's really there :)