What does a + after a username mean?

[JesusLiv3s]

Hello,

In the Who's Online section, I do see one of my admins with a + after their username, yet you can tell it's not part of the name, as it's not included in the hyperlink.

What does this + signify?

Example:

Admin's real username: Bob
Admin's username is Who's Online: Bob+

As you can see, the plus is added on to the username, but isn't the same color as the username, nor is it included in the username.

Please explain to me what this is, how I would be able to do it for myself, and any other specific information I may need regarding it. All help appreciated.