Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Graphology is the theory/science that one's middos can be deduced from one's handwriting.
Is there any source for such ideas from the rishonim or earlier?
There are modern-day kabbalists and "holy men" who claim to do such things. I'm not aware of any source for this (nor against it either, for that matter) in classical Jewish literature.