Let me get this straight, as long as I put my work on a piece of paper it's legally mine?
When it's "fixed in final form". (According to the Berne Convention)
Each draft has a copyright when it's completed; but for collecting damages on infringement cases, you need to register it with the Copyright Office of the Library of Congress.
This provides you with a legal record of when the script was completed.
There's also the trick of proving the infringer had access to the script, and proving the two works are "substantially similar".
That's why copyright lawyers make substantially bigger bucks than we do. The ones three feet by five feet, with the portrait of Herbert Hoover on them.Cheers!
Al B.