CLASS REVOLUTON is a graffito, but when it becomes accompanied by the addendum "BECAUSE THERE IS NO 'I' IN REVOLUTION" they become graffiti, though each statement still stands on its own as a graffito.

Graf*fi"to (?), n. [It., fr. graffio a scratching.] (Art)

Production of decorative designs by scratching them through a surface of layer plaster, glazing, etc., revealing a different-colored ground; also, pottery or ware so decorated; -- chiefly used attributively.

© Webster 1913