@mcc this is changing quickly, but you can still "sense" whether something was created by an LLM or not: they completely lack a sense of "elegance". In general terms, their output feels brutish. That's the reason why enforcing such a policy is hard: "the contribution must be elegant" does not translate well.
There are some papers on using deep learning models to output a probability that a piece of code comes from an LLM. I don't know if people who do not want those kinds of contributions are willing to use models to detect them.