This will just create a black market for AI generated video content that doesn't have a signature. Which I'm sure that China, Russia, hell even the US governments would not have a problem with because that would be extremely useful for them.
Honestly - not gonna be feasible to sign things that are not AI-generated. For example, my friend's phone uses generative AI for the insane zoom capability it has - so every photo my friend takes would not be able to be signed.
And this is the crux of the issue - we are beelining to a world where EVERYTHING gets an AI filter in front of it. In a few years there will be no authentic content at all.
And annoyed and suspicious techies can use it to check other people's content and report them as fake.
Yeah, there are a lot of dumb people who want to be deceived. But would be good for the rest of us to have some tools.