A "Don't Drink and Drive" campaign by Vasir breweries on their beer bottle caps. Upon opening the bottle, the car printed on the cap appears bent, and on reverse we have the simple slogan. Very simple but effective
IWC, the famous Swiss watch makers, used these stickers on the holds in airport buses to catch the attention of travelling pilots and other passengers for their new "Big Pilot's Watch".
One of the best, by Seagram, that asks drivers to choose carefully between two things:
A very simple but hard-hitting advertisement by the Mumbai Traffic Police on the importance of wearing helmet: