A sign language was a language which, instead of acoustically conveyed sound patterns, uses visually transmitted sign patterns (manual communication, body language and lip patterns) to convey meaning - simultaneously combining hand shapes, orientation and movement of the hands, arms or body, and facial expressions to express fluidly a speaker's thoughts.
In 1914 PD, xeno-linguist Dr. Adelina Arif was hired to develop a sign language which allowed humans to directely communicate with treecats by Duchess Harrington. Nimitz, Samanatha and Honor Harrington were among the first to learn it. (HH9; HH10)
- Detailed article about sign language on Wikipedia