'How do you know when a car doesn't belong on your block? "
if I have never seen it before, there is a chance the person is there for not so good reasons.
If they're stopped, they're looking for an address maybe, etc. But to pull down this back area is out of the way for most. I know when a car hasn't been there before. If they go to a driveway, cool, go see your friends, whatever.
If they're parked at the end of the block, you bet I'mma go check it out. Because an annoying busybody like myself is going to be that one deterrant from robbing a house.
Or, if they're there for legit reasons, I am happy to help them find the street they're looking for, etc.
I guess I don't understand anyone who would just look at a suspicious car on their block they don't recognize, parked with people in it, doing nothing but looking around... and just ignore it. Go talk to them. Get information. Determine if you can help, or if you can deter them from bringing drama to your block. it's called being vigilant - it could be a dirtbag house robber, it could be al quida for all you know. If every american were to watch and protect his block in this matter, crime and terrorism would plummet.
Instead, they're all content to just put their head down and hope whoever's in that car doesn't mess with them. Silly. It's your street. Protect it.