My reaction on reading the title was "o-kay...." and a pause. Then, because I will look at x-rays if you jiggle them, and movies in this era were rarely more than a couple of minutes, well, why not?
It turned out to be a young woman on a stage giving an exhibition of sign language. I will presume she is signing "The Star-Spangled Banner". It's not much of a movie by modern standards, yet when motion pictures were still in the development phase in the 1880s, one of their uses was theorized as being used to educate people in sign language. I won't say this is the earliest use of sign language in a movie; if I did, an earlier one would show up within a couple of days. I will admit that this is the earliest example I can remember. How's that for weasel-wording?