PostItNote

You don't know what a postit note is? Oh, Man! What rock have YOU been hiding under?

Postit notes are small pieces of paper, usually square, with a strip of adhesive across the top of the back.

The adhesive is somewhat strong, but still weak enough that the Postit can be removed from whatever it was attached to. However, the wonderful things about PostItNotes are: 1) they can be re-stuck countless (technically infinite, but dirt gets in the way) times, and 2) they don't leave stick on the stuff they were stuck to.

I really doubt you didn't know that, though.