It's a wonderful old french Birthday card.
It literally translates as "a thousand kisses", but is a traditional way to sign a letter "Lots of love" or "XOXO" in French.
It also refers to a particular genre of postcard - French (usually) postcards from the 1920's, usually of a romantic nature, but they can also be found for a variety of other occasions - New Year's, Christmas, Easter and "come hither" looks! Today they look (in my opinion) pretty kitschy, but they are fun!!
- first three photos were found on the Mille Baiseurs webpage -