As you know, I drive Underground trains, although a different line to the one in the article, as shaney says, not so good for the driver, I have a friend whose had three 'one unders', the last about ten years ago, he still shakes even now.
These Grafiti artists, they not only carry the paint they use, they carry wire clippers and all sorts of tools, so they damage other equipment besides painting the trains.
I don't know exactly what can be done, but I wouldn't want them dead, having said that, i'd hope that this article would make others think twice before the vandalise more trains, but I doubt it.