The sign of the horns, more sinisterly called the Devil’s Horns, is formed by extending the index and little fingers while holding the middle and ring fingers down with the thumb, signifying one’s allegiance to Satan.
The hand sign was popularized in the late 1960s by the founder of the Church of Satan Anton LaVey (see pic below).
This is Michelle Obama on the cover of the March 2009 issue of the fashion magazine, Vogue. (I circled her left hand in yellow.)
If you think he accidentally made the devil’s horns hand sign, think again.
Just try making that sign yourself. It’s not easy. It takes a conscious effort.