Basically each of these cards says "dude, can you hear me now?" A fad of the 1960's and a way for nerds and freedom fighters alike to chat around the world before the web, these cards were sent by participating amateur ham radio operators to confirm reception and are now collected for their graphics, historical content and such. I cribbed the following from Wiki, you can read ALL about them here. "QSL cards are a ham radio operator's calling card and are frequently an expression of individual creativity — from a photo of the operator at his station to original artwork, images of the operator's home town or surrounding countryside, etc. They are frequently created with a good dose of individual pride. Consequently, the collecting of QSL cards of especially interesting designs has become an add-on hobby to the simple gathering of printed documentation of a ham's communications over the course of his or her radio career"
Group of QSL cards 1961-1962 Collection Jim Linderman