Matt posted up this great idea:

One of my favorite quirks about Wikipedia is the little [citation needed] tags that users can place in an article, indicating that a dubious claim needs a reference. One day an idea struck — what statements are more dubious or outright ridiculous than those in advertisements? In true wiki fashion, the final placement of the stickers is a collaborative effort, now distributed and anonymous. If anyone sees one somewhere, please make a photo! I’ve been tagging my photoset on Flickr with citationneeded and wikiffiti — more should start showing up in the next few weeks. I’m also providing the source Photoshop file (or as pdf) for anyone who wants to print their own batch.

Wikipedia [citation needed] stickers – Link.