throwing rocks – do not

what I love about this scene is that the sign writer is pretty adamant about asking us not to throw rocks. It says DO NOT throw rocks! I’d write Don’t throw rocks. I might add a please and perhaps a thank you. But perhaps the sign writer has lost patience at the amount of rocks that get thrown into the reeds.
I didn’t see any rocks. So I couldn’t throw one even if I wanted to throw a rock.