I think this sign at the Madrid airport was made for me. I once walked into a clear glass boulangerie door in Paris. I mean, the surface was clean and the éclairs beckoned me. I could have used a warning like this.
(No, I am not in Madrid. This is from my stopover on the way to Paris earlier this summer. And yes, it is still summer for another day. It was 78 degrees Fahrenheit in New York today, after all.)