I wonder if the graffiti has anything to do with the October Horse sacrifice ritual that is dedicated to Mars the Roman god of war.
On October 15 they have a two-horse chariot race and the winning horse that is on the right side is sacrificed. Its head and tail are removed and used in two different ceremonies. Two neighborhoods stage a fight for the right to display the head of the horse.
Romans did not eat horse meat and this is the only time a horse would be slaughtered. That would explain why there's a horse head laying around to be put over a man's head on a cross. It's the wrong month for Jesus crucifixion but it's still proof that the Romans were using the cross as a form of torture in the 3rd century, once again proving JW's wrong on another matter.