The design version and date, the exact vehicle (year, make, model, color), confirmation that every phone number, URL, and word has been verified, acknowledged disclaimers (screen color vs. printed color, mockup vs. real vehicle), one named approver, and a timestamp. If the proof came back approved in ninety seconds, the phone numbers weren't checked. Full process: wraptor.io/blog/wrap-design-client-proofing.