I just mean if it's on your board then we can consider it to be yours. Works for social use cases and most other use cases.

So a Twitter clone, as long as it's pulling from each person's board then I'm not sure why bother signing the individual notes? If someone is saying "yo guys that note is injected, don't believe it" then it'd be pretty easy to diagnose, because it wouldn't exist on that person's board when you went to cross-check.

Maybe in some situation where there's a high injection risk and the impact of being misled by an injected note is quite high then sure, sign all the notes. Hard to think of such a case though.