Yeah, I would probably head for something like images and pic cards that is clear enough to both the kid and adults around and can communicate needs shortly. Signs as pics convey that better than signs as sign language since that sort of assumes prior familiarness with the sign system.
Alongside teaching him not being understood may be okay, and he will be able to get there later, but that would depend how he is with frustration tolerance and the concept of time, but something to consider? That things not working out now do not have to lead to a meltdown, and minimize from that angle.