Sorry about the sideways orientation of the first one and the bad focus on the last one, but I wanted to share the signs on bedroom doors around here.
The first door has an excellent reason for the signs and warnings.
The second door was just following the example of the first, but they (thankfully) have no rat to justify keeping people out. They do, apparently, have land mines and an easily frightened bear.
The third door is not very welcoming, but we love the occupant all to pieces anyway :)