If we deal with sings to communicate among people that cannot hear or talk, we can also look at other creatures which need to communicate without talk.
Handspeak.com has a share about the ability of dogs communicate among each other by smell as well as by signs among each other and with human. Deaf people developed signs to make the world of animals accessible to animal scientists or researchers to make communication between dog and owner possible.
An owners comment: “… I learned many signs from discussions with other deaf dog owners. Also, I have modified ASL signs for one-handed communication, since it is difficult to hold a leash and sign at the same time. …”
Interesting how an ability or disability can add new insights about other species communications.