A compromise to the ubiquitous no unsolicited submissions policy is the submission agreement. If you get a read request there’s good chance it will come with one of these. Read it. At best it’s a good initiation into legalese. At worst it’s fucking terrifying. In no uncertain terms it will say that it is in the realm of the possible that the company to which you are submitting may already have, by coincidence, a script identical – identical – to your own and therefore can produce said script without your permission.
Why would you ever sign such a document? Two reasons. One: If you don’t sign it you won’t get read. Two: These guys aren’t interested in stealing your script. They just want to protect themselves but their lawyers are paranoid savages. If they’ve got a UFO movie in development and you’re pitching a UFO movie they don’t want to be accused of plagiarism down the road. So you may think your idea is as precious as their release is scary but just remember it’s still cheaper for them to buy that script from you than try to screw you.
This isn’t just my armchair assessment. Even my entertainment lawyer has given this advice to new writers. Because when you finally do get that option agreement you’re after, the last line in that document is going to read “this agreement replaces any previous agreement blah blah blah”. Thus voiding the nasty submission paper anyway.
All this said – there are lowlifes out there. Play it safe by making sure you’re only signing submission agreements for established companies with a track record.