Many visitors to national parks today collect passport stamps, magnets, patches, t-shirts, or other memorabilia to recall their trip and to show others where they’ve been. In the 1920s and 1930s the “must have” souvenirs weren’t created to be collected at all. National Park Service windshield stickers served a practical administrative purpose; they were evidence that the automobile license fees due at some parks had been paid. Americans embraced the stickers' colorful, artistic designs, sparking a collecting craze. Drivers pasted so many to their windshields they quickly became a safety hazard. The stickers were reduced in size and eventually phased out. After WWII, the first self-adhesive bumper stickers were created in 1946, and visitors had a new way to decorate their cars and show off where they’ve been. Learn more about the sticker craze by clicking the link in our bio. Image 1: A 1920 Yosemite National Park windshield sticker featuring a cougar on the front. (Courtesy of Yose...