The dramatic increase of online shopping has fanned the flames of competition between shipping companies. Which is why, using thermal-activated ink, DHL figured the best way to advertise just how fast and efficient its shipping services are was to trick its competitors into doing it for them.
The prank was simple and brilliant. DHL hired companies like UPS and TNT to deliver large black boxes to addresses that were particularly difficult to find. But the boxes weren't actually black. Instead, they were covered with a temperature-activated ink that appeared black when the boxes were chilled to sub-zero temperatures at the time of pickup. But as they warmed up in the back of delivery trucks, the black ink faded revealing a large message on the side of the boxes boasting that "DHL is faster".
The deliverymen had no choice but to deliver the trojan packages, which were big enough to be incredibly awkward and extremely noticeable by anyone nearby. Well played, DHL. Well played. [YouTube via Tastefully Offensive]