The current models do have a specific pattern that you'll learn to recognize, but ChatGPT won't be giving you any bomb building instructions. You'll need a liberated model like Dolphin for that, and those will be easy to expose using other prompts.
The most likely outcome will be a digital "verified human" certificate, with two factor authentication on it. Bad for anonimity, but I don't see many alternatives and it may actually end up reducing online toxicity.