It may seem a strange idea today, but in the 1910s there seems to have been a ready market for postcards featuring the leap year tradition of women proposing to men. In the preparations for the Archives' move to its new location, we came across four such postcards, published by the Gibson Art Company in 1911 and collected by Gerry Boyce. (This one is the least misogynistic of the four.)
None of these were written upon or mailed, but it would be interesting to know if anyone ever did propose through the medium of a leap year postcard. You can see all four postcards on our Flickr pages, and if this topic interests you, there is an online database of Leap Year postcards which has been compiled by Katherine Parkin of Monmouth University.