Hand signals are a way to communicate and give orders to dragons. It was first introduced in the fifteenth episode of Dragons: Riders of Berk, Twinsanity, by Fishlegs. He orders Meatlug to catch Ruffnut and Tuffnut from a falling branch. Later Hiccup inquires about what he did, and Fishlegs explains to him that he and Meatlug has been working on hand signals, and it seemed to give positive results. Hiccup remarks that it was incredible, and they should start working on it right away, in the Dragon Academy