This means essentially "No through traffic", but it's posted where there are no paths or anything, just (as you can see) this tree. No passage to the land of Faerie? No hacking through the bushes and leaping off the mini-cliff where a storm drainy thing empties into the river?
Meanwhile I'm reading this piece of horrifyingly bad badfic and I can't stop. Also baking banana bread. There's no feeling of accomplishment quite like the one you get when you smell something delicious in the oven...