Why do referees do the hand signals?

Answer 1

I can't answer it, but I found an ancient newspaper article from when American football officials 1st started using hand signals. It is clear from this that (1) only a small number of signals were used to begin with, (2) very few of these have remained the same to the present (touchdown being one that did, not surprisingly, and pass interference as well; not so with touchback and clipping, for example), and (3) many more have been added since then. There must be some source that explains their origin, which the ancient article really does not.