Interestingly, before the invention of stamps, the Scandinavian postal services used feathers attached to the envelope to indicate the speed of delivery.
Such messages were officially called "pen letters" (Swedish: fjäderbrev). The feathers symbolized the speed of the bird's flight and served as a signal to couriers and postmasters that the item required immediate delivery. The feather was attached to the front of a folded letter or envelope using sealing wax.
One feather indicated standard expedited shipping. Two pens required even more speed. Three feathers mean extreme urgency - the messenger had to run with all his might.
White Feather stated that delivery was required on the day. The combination of white and black feathers gave the postman direct instructions: to carry the letter day and night.