*Donning my top hat and monocle to explain*
The "shocker" hand gesture is synonymous with the sexual move itself - the index and middle fingers extended, the third finger curled in, and the pinky finger extended, so that the first two fingers can penetrate a woman's vagina at the same time that the other finger penetrates her anus - or, as it's more informally known, "two fingers for the pink, and one for the stink." It's named the "shocker" because it's intended to give women an unexpected thrill during the course of normal digital foreplay, given that simultaneous vaginal and anal stimulation tends to be less common.