I’ll offer a rough draft based on @Mariatta 's proposal above for further feedback and iteration:
Here’s a start, covering both LLMs and other sources:
If you quote or re-post content that was originally published on another site (blog, docs, tutorial, Stack Overflow, forum, GitHub, etc) either by you or someone else, always attribute and link the original source. If another person or tool, including a large language model (such as ChatGPT or other “AI” services) is used to generate your post or a portion of it, please disclose that as well.
I’ve ripped off adapted a clarified and copyedited version of @Mariatta 's suggestions above:
If you suspect someone’s message/answer is AI-generated, there is no need to flag it as spam, off topic, etc. if it wouldn’t otherwise qualify as such, especially for a new user. Just ask where they got it from, and if they then say it’s AI-generated or taken from somewhere else, you can then remind them that to mention that fact in that and future posts following our guidelines.