Leaving a dog in a parked car is not a laughing matter. Even at comfortable temperatures cars can heat up extremely fast and turn into ovens. In some cases, when people see a dog in a parked car they will break the window to get the dog out.
Unfortunately this is illegal in some states and is obviously bad for the owner of the car/dog. One dog owner has gone viral for putting up a sign in the window that reads: "The A/C is on. He has water and is listening to his favorite music." This was a a clever way to let people know not to overreact.
On PETA's website it gives five steps that you should follow if you do see a dog in a hot car. Gather info about the vehicle (make, model, color), make other people aware of the situation, monitor the dog, educate the owner when they return, and finally call animal control or 911.
