The reg on the aircraft in my avatar is vinyl and still going strong after 2 winters. It was applied to paint on wood. Cost was about £50 from a sign maker.
Just have a look at CAP523 as I once had a letter from the CAA that they didn't like my registration marks on a PA28 I owned. I was a bit annoyed as a CAA surveyor had seen the aircraft and said nothing. It was only when I sent the picture in for G-INFO that the CAA wrote to me - lesson learned? Don't send in a picture to the CAA!
Gaz