A person on the Sailor Ranko boards posted this, and I thought people here might be interested in seeing it. This has the traditional symbols for the various planets and their biggest moons as well as some alternative symbols the poster created where there was no existing symbol or he thought a different symbol might be better.
It just seemed like this would be a good reference for people incorporating their own Senshi into a fic.
edit:
Here is a link to a similar page with a couple of variants on the symbols, including the alternate symbol for Charon mentioned below. Reference