Hopefully after all my warnings, you know not to leave a pet in the parked car even for 10 minutes. But, although we know better, I still spot pups trapped with cracked windows (or worse!) with no way to know where the guilty owner is and when she's coming back. I recall one occasion where I was so troubled that I went in to a neighboring shop for paper and a pen to write a note for the window.
Now I'm armed with these "Spread the Word" fliers from the United Animal Nations. They can be printed in color or black and white, cut up, and kept on hand for future use. No more scrambling for paper — just slip one under a windshield to make the person think twice next time without getting confrontational in the process.