1. Take pictures of his petition table.
2. Tell him you want to sign--get him to give you a petition with as many names as possible on it--and then take the petition.
He won't chase you very far if he has a table that he has to attend.
Find the closest store with a copy machine and make a copy of the phony petition. Keep the copy, give the original petition back to the people circulating it (wouldn't want to be accused of theft).
At least you now have absolute proof of fraud--take it to the State.