We have one of these and someone put a piece of a popsicle stick and wrote "Rock Concert" - Love Rock Art.Garden Trinkets - Awesome Ideas, Projects and Tutorials! Including, from 'instructables', this creative 'garden thing' project with rocks.
So you can let them out and get them in anytime you want. Or call them to safety when predators lurk. Or when you have new pullets free ranging with old flock, and need to get each flock to its own coop.