DHL figured the best way to advertise is to get their competitor to do it for them. So they tricked UPS into doing it, using thermal activated ink.

DHL hired companies like UPS and TNT to deliver large black boxes to addresses that were quite hard to find. The boxes weren't actually black. 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.

By the time they warmed up in the back of delivery trucks, the black ink had faded and revealed a large message on the side saying: "DHL is faster".

Obviously, the deliverymen had no choice but to deliver the packages. They were also big enough to be noticed by anyone nearby. What a prank. What a strategy. Check it out:  [YouTube via Tastefully Offensive]