From the RSPCA (New South Wales, Australia) comes the JustSixMinutes campaign:
Excerpt (emphasis added):
DOGS DIE IN HOT CARS: Do not leave your dog in a vehicle. Pets can overheat even when the windows are down or the car is in the shade. […]
Causing animals to suffer in any way is a criminal offence. If your dog suffers as a result of being left in a car, you can be fined $5,500 and can spend six months in jail. If your dog dies as a result of being left in a car, charges include $22,500 in fines and two years in jail.
Helpful RSPCA fact sheet concerning what to do if you suspect your dog is suffering from heatstroke: