[D]iagrams must be distinguished from indexes, which are territorial signs, but also from icons, which pertain to reterritorialization, and from symbols, which pertain to relative or negative deterritorialization. [TP: 142]
[Peirce's] distinctions are based on signifier-signified relations (contiguity for the index, similitude for the icon, conventional rule for the symbol); this leads him to make the "diagram" a special case of the icon (the icon of relation). Peirce is the true inventor of semiotics. That is why we can borrow his terms, even while changing their connotations. First, indexes, icons, and symbols seem to us to be distinguished by territoriality-deterritorialization relations, not signifier-signified relations. Second, the diagram as a result seems to have a distinct role, irreducible to either the icon or the symbol. [TP: 531]