The Spanish explorer Cabeza De Vaca observed indigenous populations in the early 16th century using sign language as an intertribal language, a highly valued language of intertribal diplomacy. A system of sign language showed up in Spain and later France shortly thereafter, and was later exported to America under the auspices of European invention.
The evidence is thin, but we do know that tribal delegations and Deaf students in Washington, D.C. were observed communicating with each other—in sign language around 1880 (Mallery 1881), narratives describing tribal sign languages west of the Mississippi being understood by Deaf students in the New York School for the Deaf in 1823 (Ackerly 1824), and there are even early 20th century films of elders communicating in sign language.
While it is difficult to know precisely how much of American Sign Language in contemporary times has roots in tribal sign languages, it can be stated that sign language is a desirable, viable, and achievable alternative, bringing Deaf First Peoples closer to an indigenous ontology than spoken English ever can.