Rubbing chin: THINKING, UNDECIDED
http://corporateicon.com/pages/428646/
Chin Stroking: This promising sign indicates that the listener is intent on every word you are saying. It's a pensive move that's usually performed by men without beards.
Chin Rubbing: This slightly different gesture, made by running the forefinger across the bottom of the chin, can indicate the listener doesn't believe you.
http://www.bemyastrologer.com/body_language_plus.html