Bloody students...! 
Better than super-glue in the lock keyways which has happened a few times.
I also like the porta-potty placed in the school prinicipal's marked parking space. [On the topic of reserved parking places, I've had a higher opinion of those principals / managers who have "their" designated special place (usually closest to the building) re-labeled for "teacher of the month" or "head secretary" or something like that. Simple gesture but shows appreciation for the people who get the hard work done day-in and day-out.]
I once worked in an FE college. The Principal and I decided to do away with special parking places. The front of the place was to be for visitors/ potential students and their families.
The Chair of Governors was apoplectic and demanded his own reserved spot - even though he was only on site a couple of days a month. Some weeks later he was in an even greater bate - a student had locked his bike to HIS sign. I’m afraid I wasn’t very helpful.
When, inevitably, I made myself redundant after Mrs Thatcher turned colleges into businesses, and him into a mill owner, I had some very childish comeback. He was always very impressed by overt signs of wealth. On the day of my last meeting with the Board, no longer an employee( lackey) I borrowed a very expensive car, put a set of made up personal plates with my initials on, and parked in his precious place. Childish, yes, satisfying when he reacted- absolutely!
