A friend of mine in Sydney, Australia, asked for help in explaining these stones. I don't know if this is really a puzzle, but he's definitely puzzled.
In one of our local parks someone has put stones round some of the trees
I can't work out if the dates, if that is what they are intended to be, relate to
And he follows up with the date-like inscriptions (Australia uses dd-mm-yyyy) on the 12 stones round one tree: