What does the + mean behind a username?

[I like Serena]

When I look for instance at the Recent Visitors of my profile, some of them have a + behind their username and others don't.

What does that mean?

I've been puzzling on it for a while and I still can't figure it out.

 

[Hootenanny]

I believe it indicates that the user in question is one of your designated "friends".

 

[I like Serena]

Hmm, just checked.
Right now I have a visitor with a + who is not a "friend"...

EDIT: Oh wait, the visitor is on my list of "contacts"!
That must be it!
Thanks! :)

 

[rhody]

I believe it indicates that the user in question is one of your designated "friends".

Hoot,

If you break friendship with them, does the + become a minus - ?!@@

Rhody...