How do you change the thing above reputation?

I’m new to the site and want to know. I’ve seen people with "onion kid" "shinigami" and some other cool stuff in my poking around. I just want to know how I can change it from "Registered User"

Settings->My Settings->Edit Profile->Custom User Title (http://forums.ffshrine.org/profile.php?do=editprofile)

Thanks!