As for Lemmy, there are many articles from lesser known sources that get positive attention here that seem to use AI but do not get removed
Well, Lemmy is not one thing, your instance for example is explicitly in favor of boosting AI-generated content. So that behavior is what I would expect if I had an account there. I personally wouldn't go there expecting to see links to human-made content.
I don't believe it's possible for human writers to write both authentically and also in a way that is coded to verify they are human (as the article discusses) that an LLM couldn't eventually come to replicate. I also don't believe it's possible for an LLM to write from their unique perspective. Therefore, I believe the strongest method for verifying ones own human-ness is to write from one's own unique perspective.
signalling humanity in a way that resists automated systems
I think I would understand your perspective better if you gave an example or two of what signals could be used?
I thought they invest any surplus into government debt securities?