A partially drawn swastika that is turned into a different kind of graffiti by the artist when he thinks he's going to get caught. This is to lessen the severity of the offense of the graffiti. In other words, an aborted effort to draw a swastika.
The teacher caught Mark writing on his desk, but found only an abortstika. Therefore, Mark only got a detention and not a suspension.
Ryan and Tony managed to make the abortstika on the gravestones when they saw the police coming. Seeing how they were caught, they might as have been making non-offensive imagery.