We did something similar when I was a senior but not near as elaborate. Our mascot was the Trojans and we only had one other high school in town, which was our rival. A few of us got the plastic forks and at night put them in the ground in the picture of a penis and scattered Trojan condems all over campus
The school knew it was someone from the other school, but nothing was ever done. A week later the other school retaliated....didn't work b/c we got out of school a week before their seniors did! *hahaha*