Well, let's start off with the basics. If you purchase a service called 'Toriprime' for $10 a year you can write whatever you want there.
If you don't , however, then you will have 'Junior member' under your name for 1-49 posts. 50 posts to 499 posts will get you 'member', 500-1499 posts earns you 'senior member'. 1,500 posts and up gets you the 'ub3r' title.
'NON-EXISTING' means the person is currently banned, and the HELLBOY user title you saw is a custom one because that person has purchased Toriprime.
Hope this clears things up a bit.