What you are seeing here is monster repellent. Z got that viking hat at Scandanavian Days, and has loved wearing it around, pretending to be a viking. Yesterday, he told me that vikings are very fearsome and scary, and if he left his viking hat outside his bedroom door, monsters would be scared to come in because they knew a viking was in there.
S thought it was a great idea. Before she moved bedrooms, we would write "Keep Out, no monsters allowed" in dry erase marker on K's aquarium. Because everyone knows monsters respect keep out signs. But now that she's with Z, no keep out signs have been written.