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QSL cards via myQSL's Flickr photostream

From the profile page:
myQSL.org is a private collection of CB radio QSL cards of the 1960's, 1970's and 1980's, mostly from Canada and the United States, but also internationally. QSL cards are personalized postcards that were used as a record of contact between CB radio (and other two-way radio) operators. Think of them as a proto-internet, a social network made of sound and paper. They are a little bit postcard, a little bit cartoon, a little bit mail art, a little bit folk art, a little bit outsider/naive art, a little bit ephemera...

These are some of my favorites, of 400 posted. He claims he has a collection of over 150,000.