Sign language
From Tardis Wiki, the free Doctor Who reference
Aboard the Ark, Monoids communicated with human Guardians by a form of signing. (TV: The Ark)
The Seventh Doctor knew sign language. (PROSE: Sleepy)
A Viyran was performing sign language to the real Charley, but she couldn't understand it, so it copied her voice to communicate. (AUDIO: Patient Zero)
