If you're like me, you probably place stamps on an envelope with little to no care for how. Well, just like me, you may have been accidentally sending love letters to business connections because of how you placed it!
The coded messages started in the Victorian era, as a hidden sign of courtship at an age where parents heavily censored mail. If you place a stamp upside down, for example, it means I Love You; diagonally, it means I miss you.
So now you know, if for whatever reason you still use snail mail, be careful how you stamp your letters. Check out more interesting info on this at the source.