“…don't bother to put a copyright on your fan fiction. 

Everyone knows it's silly to claim ownership of something based on work owned by another. It's like a car thief trying to insure a stolen vehicle, then getting mad when the cops come to take it away.

You can't protect your fan fic from plagiarists. They are cheerfully stealing from pro writers, so why should they respect another fan's work?

I'm not name calling here, just letting you know what's out there. It's a nasty world at times!

I STRONGLY suggest that if you do post fan fic that you use a PEN NAME. 

If you ever go for a career as a professional writer the last thing you want is for your real name to be associated with a copyright infringement suit! Once something is on the Net, it's out there forever!

NO editor on Publisher's Row will touch anything from a writer who has been involved with copyright infringement. They wouldn't be able to trust that the work you sent them wasn't stolen.”

Source: http://answers.yahoo.com/question/index?qid=20090912180612AAEh8pq