That is really cool, design in Adobe (or editor of your choice) onto a template created from a photo of the train, then printed on an inkjet (or colour laser) onto a sheet sticker. So simple I'm amazed nobody has done it before, now where did I store those pictures for the Advance Nankai Rap:it I wanted to use to create an Advance Star Wars wrapped train?!? 
Happily collecting things all my life...