Not to derail this into a plagiarism focused thread - I feel you but I don’t think there are many ways to add something like this to simple text files without making them way more of a pain in the ass to use - say I buy a script and want to tweak it for my own personal use as an example and that is something I do. If scripts became locked down chiefly due to one accusation that turned out to be false, that wouldn’t be great.
Also, given that the aim of a script is to mimic whats happening on screen as closely as possible, two well made scripts for the same video will naturally look pretty damn similar. Combine that with the fact that plagiarism systems look for similarities as well as exact matches (and millions of dollars are put into those systems), it seems like it’s asking for trouble on the false positive front. It only really kind of works for the spoken word because there is so much variation in the spoken word, far more than in scripts.
That being said I do understand the desire to protect your work. I just think that in this specific space, the idea of doing so is pretty far away from the practical reality.