Do you know why a horn appears on mailboxes? Messengers and postilions used a small brass horn to signal their arrival. Use of the horn soon became obligatory for the postilion, who had to know at least eight signals, each with a particular meaning: arrival, distress, departure, and so on. But what made the horn so popular was its constant use over several centuries, rather than the regulations requiring that it be carried. Today the horn is the postal emblem of many countries.