Bacon, Bennett, Azadeh Khatiri, James Palmer, Tony Freeth, Paul Pettitt, and Robert Kentridge. “An Upper Palaeolithic Proto-Writing System and Phenological Calendar.” Cambridge Archaeological Journal, January 5, 2023, 1–19. https://doi.org/10.1017/S0959774322000415.
There may be questions as to whether or not this represents written language, but, if true, this certainly represents one of the oldest examples of annotation in human history!
cc: @remikalir