There's more to tagging railroad cars than just tagging them. Taggers from one side of the country can recognize another tagger's work and they 'send' messages and designs to each other via moble canvases....railroad cars. One tagger in Chicago may recognize work from another tagger living around LA. For these artists, private property and trespassing is something that may be of concern to people like you and I, but has no meaning in their world. Walls, subway car sides, freight cars, etc. are simply accessable large-scale empty spaces to write, doodle, and paint on. It's a form of in-your-face artistic expression that purposly defies legal restrictions placed on the artists by the 'establishment'. This has also created a whole range of coating products designed to be incompatable with common graffiti materials, a couple of which I've had to look into for clients. It's a fact of urban life that I have problems accepting myself.