shirts in windows

Whenever you are driving on a highway you are bound to see a car abandoned on the side of the road with a shirt or a bag hanging out the window. What the hell does that mean? Is that something you learn in driver's ed because I don't ever recall "hang shirt from window when in distress." It can only mean one of two things, "don't tow my car, I am coming back for it", or "I surrender and I am leaving this piece of shit here!" Two very different meanings huh? Where does one get this information?