One guide that i hope is kept up to date: https://en.wikipedia.org/wiki/Wikipedia:Signs_of_AI_writing . Generally though it's a kind of pattern recognition which for some patterns seems visible to me.

I should clarify and revise my thoughts and initial comment. I do not think that not being able to detect it leads to lack of care. I actually think that many things have passed me by and in the future this will be even more as LLMs improve ("we're cooked").

As to "what do we do when we spot it" - you hit the nail on the head of the feelings I felt as I was writing the comment. What do we actually do, what can we change and should we attempt futile things?

And even the example dang gave - the actual submission as very good. Is any amount of LLM use okay and what's the level? I use LLMs at work but I don't like writing readmes or blog posts with it. But others might like writing code at work by hand and don't like writing text so use LLMs for that. Maybe I lower my expectations!