If you're suggesting I go over there and engrave the chairs and then call the police there's no way in hell. There is someone there ALL the time (especially at night) and they come outside unpredicatably. My best chance would be to wait until I see no cars and the house is dark but even then, there could still be people I don't see and there's a huge streetlight in front of their house.
I'm leaning towards a few things...
1. Child Protective Services.
Though they all look like young kids to me, its hard to tell the ages of the people living there. There is however at least one without-a-doubt minor that has permanent residence there. He is constantly being exposed to their uncouth behavior and right now, he's playing outside by those chairs. (Funny, I didn't think today was a holiday. Isn't there something called... SCHOOL!?) My aunt said it would be anonymous if we reported them and although I would hope it would do something, I don't see it having much if any affect.
2. Contact their landlord.
I don't think this is possible. I don't even know who the landlord is, though we've been told by two parties that those people are renting, we don't know if they in fact own the house or if they know the landlord. Complaining to him/her probably wouldn't do much good either. Maybe if it were rented through an agency, but not even then. Unless they're anal like Remax. Chances are it's a person who just wants their money every month, even if it comes from stolen property.
3. Say, do you know anyone who could...
The dangerous third option. Ask various people, relatives, co-workers, or even my stupid dad if they know anyone who could either mess those people up, vandalize their house, or at the very least steal our chairs back. (Not that I want them back, but neither do I want them there out front mocking me.)
Those are the thoughts going through my head though I'll probably do none due to the sheer futility of it all. Even if I did act, it'd be a different story if we had as many people over here all the time as they did. I'm also concerned about them coming over and killing our pets as a form of retaliation. They look like the sort and I would never forgive myself if that happened, even if they did get caught for it and we got all of our stuff back and then some, it wouldn't be worth it. Those are my kids.