I’ve been learning sign language for four years now, and I swear it’s fun like nothing else in the world. The only 'rationalist' aspects would come from an interest in learning neat things, and my argument that society would be better optimized if everyone knew how to sign. Finally, this mostly is just a Neat Thing. I have just tried to argue that it's more useful and enriching than you might otherwise have thought. Second, you'll obviously have to weigh up if learning to sign is worth it for you. I did okay in a one-on-one conversation with a deaf person after that. First, I actually think ASL is pretty easy to learn from the video lectures I link below. (EDIT: A few extra notes based on comments. Sign language is also super intellectually interesting in its own right and is a very fun learning experience! Anyway, on with the show. I gave a presentation on it at a LessWrong Community Weekend, and people seemed interested. I know this is pretty unlikely, but it seems worth a shot. Sorry if this is somewhat off topic, but I have a small dream of sign language becoming a rationalist shibboleth and serving as a jumping off point for sign to spread more in society at large.

Won in sign language