You need to compare opportunity costs. It’s easy to name some thing you want to do, whether learn sign language or anything else, and list the ways you could benefit if you did it. But those benefits could be rare and weak to the point where just about any other use of your time would serve you better. How often have you had problems communicating a bill in a noisy restaurant, and how much time did you lose by having to settle it without using sign language?
(Also, if those things are really problems, have you considered text messaging? If they’re not big enough problems for you to fix by using text messaging now, why do you consider them big enough problems that you should learn sign language to fix them?)
These can shade into each other or be indistinguishable. Suppose you’re trying to signal that you’re smart. Is this #1 or #2, depending on how smart you are? If you think you’re smart and you really aren’t, and you’re intending #2, does that still count as #2 or is it #1 instead?