"Things You Wouldn't Know If We Didn't Blog Intermittently."
The guy who posted it at reddit is the photographer. In his comment history, he tells about making the sign, and forgetting it in his car.
I'm always reluctant to credit things to Redditors, because reposting is so rampant there. In this case I searched Google Images and saw the concept was old. But apparently the label and this photo is new. Text modified. Thanks, Miss C.