Good thing he finished before the tram was needed during rush hour

... Why the downvotes tho ? Tagging a tram is NOT ok. Chaining a kid to a tram is NOT ok either. There are legal ways to handle this kind of thing, and things such as court mandated community service are a thing.
Taking justice in your own hands is the stupidest way to handle this problem.

Nope. That's perfectly ok. He lost the right to not get chained to the train when he vandalized it.

Yeah, that's absolutely how the law works. They also had the right to flay him. They could even have sold his kidney.