As I mentioned earlier, Abraham Arcavi is looking for references on the history of graphic representations in mathematics. The history of graphic representations (such as diagrams, maps, charts, ...) ranges from stone carvings to computer visualizations. Please, don't be shy ;) and do suggest pointers. (Did I tell you before that I was characterised as a "shy historian" in an recent article of the Bulletin of the BSHM? :)
This may not exactly be what Abraham is interested in, but Reviel Netz gave a talk on "Greek Diagrams" at the Third International Conference for the History of Greek Mathematics, Delphi, August 96. A few years ago, this talk was available on the Net, but it seems now that those links are no longer available. Netz also wrote an article entitled "Greek Mathematical Diagrams: Their Use and Their Meaning" in _For the Learning of Mathematics_ vol. 18 (1998), no. 3, pp. 33-39. [Abstract: Greek mathematics relies on diagrams in an essential, logical way; diagrams are not just pedagogic aids. Before writing down a proof, Greek mathematicians would have outlined it orally in front of a diagram. For them, letters were indices, not symbols: the identity of the object was visual. In Greek mathematics the diagram occupied the place of conceptual systems in modern mathematics.]
As indicated earlier on HM a few years ago, , Reviel Netz wrote a book, "The Shaping of Deduction in Greek Mathematics" which includes a substantial part of the above.
Again, the following link may not exactly be what Abraham has in mind, but [HM] listmember Fulvia Furinghetti has co-authored a paper entitled "Revisiting Guided Reinvention: Icons, Indexes, and Symbols in the Construction of Mathematical Objects", in which she discusses various types of signs (mainly icons and geometrical figures) used by students in constructing mathematical objects and in proving.