I absolutely LOVE postcards with slogan postmarks (postmarks that publicize something in addition to the usual information). Some of those postmarks can be quite spectacular and detailed all by themselves.
One of my all-time favorite postmarks is on a Swiss postcard mailed in the 1930's. The postmark encourages the use of airmail and shows a very old airplane. The postmark was applied to a stamp that showed a lake surrounded by mountains. The way the postmark was applied to the stamp made it look like the airplane was flying above the lake and coming off the edge of the stamp.
I am actually one of those postcard collectors that prefers postally used postcards over unused ones. With a postcard that has been used I feel like I am looking at an historical event in addition to whatever is portrayed on the card, and enjoy looking at the stamp, postmark and message area. I have learned additional perspectives from used postcards. In some cases the sender of the card adds information from their own perspective relating to what is portrayed on the front of the card. One postcard from what was then Yugoslavia simply identified the picture side as being in Kotor. The sender added a comment that the wall shown on the postcard had been built hundreds of years ago "to keep the Turks out". Some of the postmarks also provide interesting information and perspectives such as slogan postmarks from past wars encouraging people to buy war bonds, etc.
On another forum at another web site one participant bemoaned how hard it was to find postcards with slogan postmarks as none of the sites have such a sub-category for postcards. That is why, when space on the description line permits, I try to mention "with slogan postmark" or something similar when I offer such postcards for sale here or elsewhere. I also make sure one of the photos with the listing is a close-up of the slogan postmark.
