I was thinking about how well sign writing paint adhered to vehicle paint finishes. Working in a garage back in the 70's we would sometimes get vans in for respraying which had been sign written. When a sign writer came in to paint a vehicle there no preparation done apart from cleaning it . The singwriter would set about marking it out and then painting it . Years later when the vehicle was resprayed the writing would be rubbed down with orbital sanders . The paint was stubborn and wouldn't flake off. Once flat the van would be sprayed , all nice and shiny but with the ghost writing would be still visible when looked at carefully .