My HS class had a great prank...
Parking for the seniors was limited to a small lot (that fit about 20 cars) next to the woodshop. It was a little closer, but not much. To make matters worse, the faculty always blocked us in when we left after school, so it made it difficult to leave.
We live in the country, so just about everyone knows someone who has access to (or has access to themselves) large farm equiptment. One day towards the end of the year, we arranged it (quietly) a couple days in advance so that on a Friday, we'd all get up early, hop in our farm equitpment (which we had located at the house closest to school (mine)), drive to school in it, and parked the teacher lot full. The rest of the seniors (who were driving) were instructed to NOT park in the senior lot that day. We pulled the keys from the farm equiptment, hopped in some spare cars, and drove up to the local diner for breakfast. Someone had made a sign reading "New faculty lot" and put it up by the senior parking lot.
It was great. They couldn't tow the farm equiptment, so the faculty was forced to park in our lot. And at the end of the day, they were blocked in by the train of farm equiptment trying to leave the school. And did I mention combines and tractors are pretty slow?
They took it pretty well. They had been expecting something much more damaging, so they were releaved when we didn't break anything. All in all, it went well.
Alternativly, you could probably get there early and spell out 2002 with your cars in the faculty parking lot. Just make sure the faculty has a place to park, cause they'll get pissed off if they dont