I recommend you put a NO PARKING sign on your ceiling and an OPEN sign and BUSINESS HOURS sign by your door.
Years ago in college this sign was in a lab room and I later made one for my classroom. It scared some kids and irrated some parents. "Caution- On going axial rotation. Occupants subject to spatial temporal dissassociation and momentary lapses in continuity of logical thought. Association my be contagious. Enter at your own risk". It means the world is turning and you may get dizzy.
This and the aformentioned signs makes for fun comments.
It helps you find out who has a sense of humor.
I hope this helps,
Love to Teach and Teach with Passion
Remember...It's not Magic, It's Science