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It's pretty easy to prove that work is your own on the cheap by simply mailing your scripts to yourself and never opening them unless trouble brews. The envelope will be stamped with the date the post office received it - keep these envelopes in a safe place.This sort-of works. It might hold up in court. Seriously, filing for copyright is cheap. Get the forms online, print them out, fill them out, print the work, send it in with the $20 fee (or whatever it is now.)
It's pretty easy to prove that work is your own on the cheap by simply mailing your scripts to yourself and never opening them unless trouble brews. The envelope will be stamped with the date the post office received it - keep these envelopes in a safe place.It doesn't stand because you can send youself an opened envelope. It will have the date stamped but they'll never know when you closed it. You could claim anything with that move and that's why it doesn't work.
Anyhow, what I'd look at doing (if you don't want to spend money), pop it up online and look into the "Creative Commons" copyright:
http://creativecommons.org/
I haven't gone through it (I'm not a lawyer), but it'll likely hold up more than a mailer...