A fairly new dog training specialty, but one that is taking hold, teaching your dog to respond to you using buttons and to talk to you using the same buttons. While it is not for every dog, with patience and focus you can actually train your dog to communicate with yout.
Yes both dogs and cats can learn sign language whether they or their owners are hearing impaired or as a quiet means of commands that allow humans to communicate with their pets. Start with basic commands and expand if your pup embraces the process.