I'll be honest, I think this is a social issue that you're trying to apply a process-solution to solve.
If someone writes "this was completely hand-written with no AI assistance", I'll just believe them. I'm already committed to letting your words fill my brain for a bit, so I don't know why I would NEED a cryptographic signature to PROVE you aren't lying about WHO wrote it.
Being called out as a lier will be a LOT more painful than 1) using an LLM to write quickly and not lying, or 2) doing what you claim to be doing and writing it with your feeble, non-metallic human hands.
(First version of this comment had an example from an HN thread of this SPECIFIC behaviour getting called out but ehh that’s not the right vibe. My point is it does happen.)
That's actually a good point. Plenty of people just want to let their beliefs out in public. And there's not much benefit to lie about AI use. Some people use it and some people don't, and it's two very different groups of people.