Train graffiti, the harmless way

This is clearly one for the older kids, or indeed, perhaps the rebellious parents among us: a model train, together with transfers to help you graffiti it up, just like the real underground trains you see in town every day. You could look at this two ways, I guess - maybe you don't want to encourage such anti-social behaviour as train tagging in your child. But maybe, just maybe, this'll provide an outlet that's easier than actually going out and decorating the real thing. Either way, you end up with a pretty cool ornament.