Signals for cruising: foot tapping, sometimes they'll slide their foot closer and continue tapping. You should watch for shadows moving as well, sometimes tapping is just tapping. Sit a bit forward on the seat and jerk off to create moving shadows, if the guy next door looks down he'll see it and maybe initiate it (he could be doing this too so pay attention). Sometimes a little cough works to see if he's interested. Play close attention. Don't force it. Be discreet. And stay safe.