Its possible to use Special Characters in-game, I trialed some as badges for ranks in-game but decided on keeping it simple, Some crews may want to replace long rank names in their crews with Symbols or add badges to ranks in their crews. You can also use these symbols in chat and on signs.

This is a great website to copy and paste symbols http://www.copypastecharacter.com/all-characters

These are a select few I picked out and trialed as badges on PirateCraft a long while ago, that might be helpful in picking badges for your crew mates.

⟫ ≫ ⊱ ⋙ ♜ ⚔ ⚓ ⎈ ✒ ♰ ✉ ✙ ✚ ✜ ✛ ♰ ♱ ✞ ✟ ✠ ✢ ✣ ✤ ✥ ✦ ✧ ✩ ≗ ≘ ≙ ≚ ≛ ≜ = ≡ ≣ ⊵

Remember you can also use color with these http://wiki.ess3.net/mc/

So as an example:

/crew setrank GodsDead &a⚔ &5Guard

Would look like this: