A Musical Notation

Consider a culture of polyphonic improvization where the conductor has a sign language, using the position of the left and right arm to communicate what two of the voices do (probably the middle ones), and the left and right hands to communicate what the top and bottom voices do. Reading the middle lines' meanings requires being able first to read the top and bottom line symbols, because the arm position basically communicated how the middle voices' movements relate to the top and bottom ones.

This system is later on turned into a notation system, whereby each symbol consists of partial symbols for arm position, arm movement, hand signs and so on, so you basically get a series of very stylized 'conductors', with each conductor representing a pulse of the rhythm. Omissions of partial symbols may either mean 'silence' or 'continue previous pitch', depending on stylistic conventions. Sometimes it is unclear which is meant.

Notation for dynamics are done by simply bolding or weakening the lines - this does not, though, communicate which particular voice(s) is (/ are) strengthened or weakened.

As in most conducted musics, the facial expressions and other aspects of body language are interpreted by singers as well, and may sometimes be expressed by stylized faces inserted before a symbol. There is a convention as to what direction the eyes of the stylized faces are directed to direct an instruction at some particular voice.