1. Would you think it was suspicious or possibly stolen, and call the cops and report it?
Say you did call the cops and report it, and they came by and said "it's legally parked; what's the problem?" and drove off without investigating it. So the car continues to sit there in front of your house with the key in the ignition and the windows down... for three days.
2. Would you get curious about the car?
3. Would you start wondering if there was a body in the trunk, or a bomb, or think up any other imaginative scenarios for why the car is there?
4. Would you take a peek in the car to see if you could find any contact information for the owner?
Say you did take a peek, and it turned out the car is actually a "bait car," filled with surveillance equipment and left there by the police to catch car thieves. And when they see you snooping through the car, they show up, lights flashing, cuff you and charge you with burglary of a vehicle. But since you have a clean record and seem like an honest guy/gal, they offer you a deal: deferred prosecution and no penalty as long as you sign a confession and don't commit any crimes for a year.
5. Would you take the deal or get a lawyer and fight the charge?