Last week I saw this on the rear window of a car. God help us.Here are some more musings on this "weird form of modern folk art."
Here's what Wikipedia has to say on the subject:
A likeness of Calvin appears on a set of decals with an arrow to signify urination. These are bootlegged images that became widely popular, and are disliked by many fans of Calvin and Hobbes because the images are contrary to the actual themes and atmosphere of the comic.
The original image shows Calvin filling a water balloon, not urinating.
The image of Calvin is here used in reference to his mischievousness. This constitutes one of the many copyright violations the strip has generated.
Another set of bootlegged decals show an image of Calvin genuflecting before (usually) an image of the Christian Crucifix. Ironically, this particular image of Calvin is taken from a strip wherein Calvin is offering a bowl of tapioca pudding to his television set.
