Blame Detroit.

The bumper sticker apparently originated with the introduction of the Model A Ford in 1927, according to brief histories on the Internet. The predecessor Model T lacked bumpers, which were added as a safety improvement. Made of cardboard and metal, the first bumper stickers were attached to the bumper with wire and string. The great technological breakthrough is usually attributed to Forest P. Gill, a silk-screen printer in Kansas City, Mo., who in the 1930s printed messages on canvas, a change that led to the use of adhesive paper.

Read the full story in the Washington Post.

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