The episode, “The Sound of Bleeding Gums,” focuses on Lisa Simpson, who discovers that her hero and favourite musician, the late saxophonist Bleeding Gums Murphy, has a son who’s deaf and needs a cochlear implant.
Although humans in the “Simpsons” world only have four fingers to a hand, they’ll use American Sign Language in the episode.
https://www.huffingtonpost.co.uk/entry/simpsons-deaf-actor-sign-language_n_62531a5fe4b0be72bfea7a3b