Hmmm, I had a history professor that used to give a little speech when handing out test papers:
He would say, "If you notice a typo, and you truly can't understand what is meant by the question because of the typo, please point it out so that I can clarify for it for the rest of the class. However, if you notice a typo, and have no other reason to point it out, other than to show the rest of the students that I made a typographical error, please refrain".