Check out this website:
http://m-rank.netIt tells you which vector illustrations sell well on Shutterstock. I remember a guy doing Arabic calligraphy and he used to be somewhere among the top 100 contributors, but I can't find him right now. I've also seen people selling simple motivational quotes ("be strong" "don't give up") written in beautiful handwriting, and they often rank quite high. If you're good, I believe it will sell, since quotes and calligraphy can be used for multiple purposes.
I myself have no experience with calligraphy, and I cannot tell you how they sell compared to logos - but I think you should give it a go
