Earlier this year I heard about a carved scar on a tree outside Wagga Wagga.
I went looking for it while I was staying in the area over Christmas and think I found it.
I've heard that carving trees was a Wiradjuri custom to remember the dead, which might explain why the shape doesn't seem like those I've seen elsewhere for coolamon.
The horizontal lines appear to be evenly spaced apart, which suggests a deliberate design but I'll ask around and see what I can learn.