Any polyurethane worth it's salt if properly applied wont' wear out for a very long time. If you want the markings permanent make them polyurethane. Adhesive markings would be good if you think you may sell the ship in the future to someone who may not want them (or, if exported, it goes to a country where the airworthiness doesn't allow them - I've seen a few glider type certificates which still have the "must be white all over except for national registration marks" in them with no provision for additional coloured markings and seen this interpreted by officials as meaning the markings are prohibited!)