Braille is protected on the grounds of free speech, even though it's not commonly used. It's a form of speech since blind people must rely upon Braille in order to "read" items. Braille is not too common, but thousands of people rely upon it each and every day in America.
Braille isn't speech, true, but it is a form of communication and it is the way that many blind people choose to communicate with each other in a non verbal form. Freedom of speech also protects us when we write things down on paper or the Internet, so it only follows that Braille would be the same.
Braille is the same as writing - only, in this way, taking the writing into 3D for people who cannot see other writing. If free speech laws apply to writing in general, which it does in many aspects, than it should equally apply to Braille. Not doing so is strange and wrong.
Braille is a form of written expression, so it should be protected under the same ground that written speech is given. Braille is simply the written language for the blind, so it is still a form of speech. I have not heard of any cases where it is not being protected.
Braille should be protected on the grounds of free speech, because it's a form of speech as legitimate and valid as any other. To not allow it the same freedoms as the spoken or printed in ink word would be extremely unfair to the visually impaired. It doesn't make any sense to restrict it.