Hah. After reading about Plains Indian Sign Language I fell into this wonderful rabbit hole about sign languages, such as Harem Sign Language: A Tool of Power in the Ottoman Empire:
Today we’re diving into the fascinating story of Harem Sign Language, also called Seraglio Sign Language, from inside the Ottoman Empire. This wasn’t just a way for Deaf servants (dilsiz) to communicate — it was the everyday language of the harem and the palace, used by sultans, women, and guards for hundreds of years.