Actually, both well-defined and temporary signs, as well as sign systems and specific media productions and works of art, can be said to share a lot of properties with and, hence, also overlap with other signs, systems and types.(pag 1)

It has a material interface. The reader of this Introduction is probably confronted with some sort of flat surface: a paper, hopefully in a book, or a computer screen. This kind of material interface allows for a variety of appearing content. You can put almost anything in a book, as long as it is flat and static, and you can put almost anything on a screen, including things that move, as long as it is flat. (pag 1)