How to Flirt With a Handkerchief, 1877

"I hate you"?
George P. A. Healy, Euphemia White Van Rensselaer (1842)
Metropolitan Museum of Art

"The handkerchief, among lovers, is used in a different manner than its legitimate purpose. The most delicate hints can be given without danger of misunderstanding, and in "flirtations" it becomes a most useful instrument... The following rules are the law on the subject:  

Drawing it across the lips                       Desiring an acquaintance
Drawing it across the cheek                  I love you
Drawing it across the forehead            Look, we are watched
Drawing it through the hands               I hate you
Dropping it                                                   We will be friends
Folding it                                                       I wish to speak with you
Letting it rest on the right cheek         Yes
Letting it rest on the left cheek            No
Letting it remain on the eyes                You are so cruel
Opposite corners in both hands          Do wait for me
Over the shoulder                                     Follow me
Placing it over the right ear                   How you have changed
Putting it in the pocket                            No more love at present" 

Daniel R. Shafer, Secrets of Life Unveiled (1877) 

It would be pretty easy to confuse "I hate you" with "Do wait for me," and your lover will be heartbroken if you ever have to blow your nose, but still: the time has come to apply this system to bar napkins.