I would assume it's owned by someone, seeing that it's on a metal pole, and is actually taken care of. No doubt vandals would've destroyed the light long ago if it was abandoned.
I would leave that light alone if I were you. Sure, it's a cool light to look at and have, but I'd leave it like that. Not worth getting in trouble with law for something that still works and is on every night. Plus you get to see it lit.
At the very least you should ask the owner if you can have it or could swap it for a different light like a LED light and do it the right way.