TFA is talking about C2PA, a regular signature in the meta data. A lack thereof means nothing, but if it's there, the false positive rate should be near zero.
Yes, but I also think it will be trivially by-passable if you pass your output through another LLM. At least for text.
It might help catch students cheating, but not real spam-bot usage. As soon as platforms start checking for watermarks spambots will add anti-watermark passes.
Any attempts they use are defeated by a text editor and CTRL SHIFT V. Unicode characters are no new thing.
Reminds me of how people tried to argue that NFTs aren't anything more than just jpegs.