Postage stamps used to convey messages of love:
On philatelic and auction sites you sometimes find postcards which illustrate with small pictures, similar to naval flag signals, what it means if the stamp was stuck in this or that position on the card. The custom is probably as old as the greeting card itself, which started its world conquering tour from the Austro-Hungarian Monarchy in 1869. … The new fashion spread rapidly, and after the turn of the century the rules of the language of stamps received their particular chapter in the etiquette books along with the languages of flowers, handkerchiefs and fans.
Steve Delahoyde laments, "Turns out I've been unintentionally saying "I love you" on all the bills I've paid over the years."
The Dish 