In the Mod game, actions are laid out on a circle. Each round, players choose an action simultaneously and gain points for each player they are one step ahead of in clockwise direction. Cooperation is rarely used. This article facilitates cooperation and deceit by adding a signalling phase where one player signals which action they will play. Our novel Mod-Signal game lets players cooperate by adhering to their signal, but they can also lie by playing a different action. In our experiment, humans play the two-player 24-action Mod-Signal game with an agent and with each other. While cooperative play is faster and yields more points, players predominantly lie and play non-cooperatively. Furthermore, our participants usually use no more than second-order theory of mind. While the Mod game is mainly played competitively, our Mod-Signal game can also be used to investigate cooperation and deception in the context of theory of mind.