In his book (1ed. 1969) Languages of Art, Nelson Goodman treats Labanotation as the most important dance notation system. It gets a thorough examination based on Goodman’s theory of symbol sytems. All in all Goodman considers Labanotation a fairly succesfull notational system, comparable to a music score.
Unfortunately, the philosophical concepts Goodman uses in his book are often beyond my current comprehension (and I was not interested enough to dig further). Perhaps I will return to the book later, since it did seem to offer some solid ground.
He does not say much about gesture and nothing about sign language. The only bit I recall is about the use of stylized gestures and Mudras in dance, which are opposed to modern (disco) dancing which does not denote anything (but the rhythm of the music and prior performances of the moves?). Languages of Art is based on Goodman’s John Locke Lectures of 1961/62.