To be transparent, I'll preface this answer by stating that I'm an outsider to this site and community. Sue VanHattum (mod) suggested it might help if I posted giving some ideas, which is why I'm posting here. While I have experience working with and addressing LLM-generated content on the Stack Exchange network, I'm unfamiliar with the Math Educators SE site beyond taking the tour and briefly interacting with one of your (diamond) moderators in chat.
Consequently, these are ideas based on what I've observed on other sites, not based on your specific community. What works well on one site doesn't necessarily help another. I also don't have hard/conclusive data to give you that demonstrates these will work or help. It's also not guaranteed that even if you agree with the suggestion, Stack Exchange (the company) can or will do it for your site. Still, I hope these are helpful, but please ensure they meet the needs of your site.
Tour page warning
Diamond moderators could, after reaching consensus via Meta, edit your tour page to include a note such as the following (taken from Ask Ubuntu). You'd want to change the link and site name. I also don't know how many users actually read (and follow) the guidence in the tour.
Please also note our policy on AI generated content on Ask Ubuntu.
A dedicated help center page
Stack Overflow has a Help Center page explaining why LLMs (like ChatGPT) are prohibited. If y'all agreed on what to put there,you could request something similar. Similar to idea #1, this relies on people reading a page.
Answer box reminder
The above two options are more useful for people that "read the friendly manual", so to speak. Another option is that when a user uses the answer box, a warning is added to the answer box reminding them of the policy. See this Meta Stack Overflow post for what Stack Overflow did.
Featured Meta post
Some sites (Ask Ubuntu, Stack Overflow, and possibly others) have a featured Meta post (i.e., with the featured tag) reminding users about it. This means it appears in the right sidebar (or the bottom, on mobile). This also requires a diamond moderator to reapply the featured tag, as it will disappear after a month (30 days?).
I hope some of these help. Feel free to leave a comment here or ping me in chat with further questions or if you'd like clarifications.