Ben Bernanke is showing us a sincere but suppressed smile in this image. His eyes, particularly his lower lids are great examples of the specific configurations we should always see with an authentic smile of joy-happiness (see Secret # 353: Brad Pitt's Smiling Eyes - Sincere and Insincere Smiles). The mouth component of his smile is suppressed - not being opened. The primary reason he is smiling it is directly related to what his left hand is doing - specifically the middle finger. The FED Chairman is flipping off whoever is speaking.
An Emblem is a specific body language term for a signal that is recognized within a region, culture, country - or in this case worldwide. Its meaning is non-ambiguous within that described region. But emblems can vary from culture to culture, etc. - so great care must be given so as to not misinterpret their meanings. An emblem may be a positive in one country and quite derogatory in another. A Partial Emblem is a modification of the complete emblem - such that it is displayed in a not-traditional location. It is also common for partial emblems to be displayed in fragmented form - i.e. not fully unfurled. A Partial Emblematic Slip (PES) is a subconscious display of an emblem which often contradicts the words being spoken.
Note also the force being applied by Ben's middle finger to his left temple region. It is displacing the skin and underlying tissue easily 1.5 cm or more. This signal of force speaks to the amplitude of his negative emotional tone. If his finger were a pencil, it would have broken.
Here, Mr. Bernanke is displaying his smile in unison with giving the Bird. Thus his smile is a variation of "Duping Delight". The Chairman of the Federal Reserve Bank may be smiling for several reasons, but the primary (perhaps only) one is that he is fooling (duping) the speaker - giving him a profane gesture in a camouflaged manner. Ben is sincerely happy - yes ... but not for the usual reasons. When a partial emblematic slip is displayed in the company of language with which is not congruent - always believe the body language. In such scenarios, the PES is a highly reliable method of deception detention (Ekman).