Lehrer: "John, are those crib notes in your pocket, or are you just happy to see me?"
Yes, a 4" x 6" rectangular white pen.
Given, the quality on the video Drudge linked to isn't very good. Try this video link, and zoom to Full Screen. You will see very clearly that it is NOT a pen.
http://www.boston.com/news/special/politics/debate_video/sept29/1.html