A signal is something you use to discern something in lue of direct information. In the case of docs, just look at them and if they suck, or are good, it doesn't really matter where they came from. That being said, Ill take AI generated docs over no docs, and no docs is very common.
How do you know if you can trust then if they are human generated? Your trust the people. AI isn't going to jump and just generate docs, a person has to prompt it, and you should expect the person to proof read and correct it. If the person turns out to be untrustworthy, you stop trusting them.
