Cluechalking

If you're familiar with the idea of warchalking, then you'll be pleased to hear about the variant that codepope describes: Cluechalking!

Tired of trying to figure out if someone has a clue? Let me introduce cluechalking. Come across someone who is particularly clueless? Cluechalk them with a 0 in a circle. It shouldn't be too hard. As they are that clueless, they won't notice you pulling a bit of chalk over their forehead. For best effects though use a permenant marker.

Update: Add this to your interests list or see who else has (good idea, wechsler!)