RMS Titanic

When the Titanic was certified to carry mail, it was assigned the prefix R.M.S Titanic which stood for Royal Mail Ship.  She had a mail hold below decks which carried thousands of parcels of mail and 5 postal clerks were assigned to sort through the mail during the trip and ensure they were transferred to the US Government for mailing when they got to the United States.  Of course, with not as much to do on board for fun, people often took to writing letters to friends and family back home to update them on their lives or tell them of the exciting voyage.  The White Star Line was happy to accommodate them by selling postcards in the barber shop and having stationary available.  The mail room was one of the first rooms to flood when the Titanic struck the iceberg and none of the postal clerks on board survived. 

This envelope dated 1912 has a White Star Line burgee on it, showing something similar to what was used on the Titanic with stationary so you could send letters to loved ones, telling them of the voyage.  Inadvertently, they would act as advertisements for the White Star Line should their friends want to travel too.