When your concept was safe and secure inside your own head, you were probably anxious to finish the script so you could run to Kinko's and give copies to anyone on the street who might read it. Now that you've typed "Fade out" on the last page, suddenly you have this desire to lock your baby safely in a drawer in case someone likes it too much and you too little.
The stealing of ideas in Hollywood is not rampant, despite the occasional high profile case. Some 17,500 screenplays are registered with the Writers Guild each year, and how many cases of theft do you hear about in any one year...few if any. The fact is, if a producer likes your idea, the producer may want to nurture a relationship in order to be in line for your next original thoughts, not alienate the golden goose by stealing your idea. That being said, it isn't wise to go into any relationship unprotected. When your script was just a casual collison of the left and right side of the brain, it wasn't protectable material, but as a screenplay, even a treatment, you have a couple of options.
The U.S. Copyright Office
Form PA
Material "created" after January 1st 1978 is automatically copyrighted, BUT, if you ever go to court you'll want the extra protection that registering with the copyright office affords. It only costs $20 and is good for your life plus fifty years. The Copyright Office has an excellent web site that outlines what is copyrightable, what isn't, and how to register your material. Forms and instructions on how to fill them out are available to print, although to do that you'll need to download a free copy of Adobe Acrobat Reader available via hyperlink from the copyright forms menu.
Nothing seems to give a title page more caché than "Registered WGAw", although you rarely see the actual registration number that should accompany it. It's popularity may be due to the perception that the material has been given an industry stamp of acceptence, and that the writer has joined a club with member privileges. In fact, for the twenty dollar registration fee, the registrant is entitled to no other benefit. In addition, if you register your script through the Writers' Guild, you'll have to set your computerized day planner to give you a reminder to reregister every five years for another fee.
Poor Writer's Method (not recommended)
Send yourself a copy of your script via registered mail and keep the unopened envelope in your files. Personally, with millions of dollars at stake, I would find it hard to believe that any court would award a writer damages based on such a low-tech method of establishing authorship. People have forged more complicated things than a postmark.
Also, a writer should also keep submission records to keep track of who read their scripts when and whether the script was returned. In the unlikely event a clone of your script is released, you'll need to establish that the producers had access to your script. With the shifting nature of film personnel, this can be difficult at best, so keep detailed records.
1 Approximately 30,000 items are registered with the Writers Guild each year broken down as follows: Film scripts 7,500, film treatments 7,500, and a combined 15,000 for teleplays and TV treatments.