Volkswagen's new city car is only 3 centimeters long.

(click image, via)
Actually the new up! is 3.5 meters long. Yes, that's a real up! on a wall in Paris. Will probably earn some awards, if not sales. The car just went into production last month, according to Wikipedia. An electric version of the up! is expected in 2013. Ad agency: V. Paris.
Previous real car billboards:
• Mini in Milan.
• Don't Drink/Drive in Madrid.