Amateurs!
OK since most of you are giving "dorm" pranks, here's one for a house.
Go buy a bag of Turfbuilder lawn fertilizer. Sneak over to the house about 2 am. Using a drop spreader, write a "message" in the lawn (use some creativity here fellas). In about 2 weeks or less, your message will appear when the fertilized grass will become a darker green color than the surrounding grass, and last for weeks.