DHL’s large network of offices, trucks and employees, makes it faster than most of its competitors. To communicate this through an ad campaign is an expensive proposition. So they got German trojan campaign specialists Jung von Matt/Neckar to make their competitors (UPS, TNT and DPD) unknowingly promote them as the fastest packet delivery service.
Large inconspicuous packets were created and sealed with thermal foil. On being cooled in large refrigerators these packets turned black. UPS, TNT and DPD were then asked to deliver these packets to difficult but central city locations. During delivery these packets were exposed to the warm city temperatures and this caused them turn to yellow and expose the words “DHL is Faster”. 😎