(Not OP)

This would work for videos that people want to acknowledge as their own, but they could just tweet out they own it for the same affect.

The issue this tackles is videos that people don't want to claim ownership of, e.g. if a video emerged of <insert politician here> kicking a child, the politician can't say "I haven't signed it therefore it's not mine", instead we need tools like the above to be able to say, "this is faked, do not trust it".