I like to copy and paste special characters straight off other pages (if I get the urge to use special characters at all). They will often register here. Codes like [b] and [sup] (by no means a complete list) accomplish the rest.

In some cases with sigs/posts they will make the fancy content in another program/on another site and turn that into an image, but I suspect that isn't what you are getting at.

http://www.roleplayerguild.com/topics/143069-symbols-characters-bobs-and-bits-useful-for-creating-titles-and-pretty/ooc is a decent reference section.

Various functions work differently and are unfamiliar/missing/extra because this forum wasn't based off an existing engine, but built up almost exclusively by Mahz (with some additions from github suggestions).