In college we had a philosophy club that met at a bar downtown. We spend the colleges buck to buy pitchers of beer, and bottles of wine. Oddly the faculty didn't like our use of funds, so we had to become the un-school-endorsed "philosophy gang", to continue drinking on the school's time (never mind that they had an on-campus bar, and we went out to the bars with the chair, and faculty), so we had to invent a gang sign. This was it. (mimes stroking the chin in deep thought)

Sadly we felt that this would make our female philosophical gang-bangers feel bad, so they had to tap their forheads thoughfully.