J.D. created a 'petition' before the Westerburg High bombs, and he used Heather Duke's power to get it around the school. But he couldn't leave the note, due to the bombs failing and killing him instead after Veronica's intervening.
There is differences from the movie's petition and the musical's petition.
In the movie, the mass-suicide note is a petition. Students believe they are signing for many things, like Big Fun playing at their prom, a hot tub in the cafeteria, etc.
He reads the petition to Veronica after he climbs into her room and discovers that she has hung herself. But Veronica disguised it, and was awake and listening to the note. The following day, she goes through the school without J.D. seeing her so she can stop him while he's setting up the bombs in the boiler room.
"We students of Westerburg High will die. Today. Our burning bodies will be the ultimate protest to a society that degrades us. Fuck you all!"
In the musical, the petition is to get a holiday to remember victims of suicide. Like the movie, Heather Duke helps circulate the petition to everybody in the school, and it still has the same intentions of it being a mass suicide note for when J.D. blows up the school.
He reads the petition to Veronica after he breaks into her house. Earlier, Veronica had broken up with him, and J.D. comes to her house to look for her. But Veronica barricades herself in the closet, and J.D. reveals the suicide note and how he originally planned to kill her; saying that blowing up the school was the reason why she broke up with him, since he believes that the students have brainwashed Veronica. He grows increasingly crazed and impatient, and finally breaks open the closet door to find Veronica hanging by noose. The rest continues like it does in the movie.
"We, the students of Westerburg High will die. Our burnt bodies may finally get through to you. Your society churns out slaves and blanks, no thanks. Signed, the Students of Westerburg High. Goodbye."