That's a really old autopen. Did you know that Jefferson used one a lot. The cam is the heart of the idea. There is a corresponding "recorder" that has the same arm mechanism but is driven "backwards". The writer holds the pen and writes while a recording wheel is turned and the cam shape is written on the wheel. The cam is then constructed from that. Newer autopens (like from the 1930s) used groves like a vinyl record. Of course today, it's just an image that is printed and there are companies that will make fonts out of a person's handwriting.