In Archeofoss 2020, Michele Pellegrino and Donato Coppola presented their analysis on Prehistoric engravings and graffiti, like proper artistic events, which are fundamental to understand characters of the graphemic-symbolic system shared by groups of hunter-gatherers of paleo-mesolithic culture (see the abstract in https://zenodo.org/record/4002961#.YHgzlOgzaUk).