The linguist Geoffrey Pullum is really onto something here, explaining the mindset that results in off-kilter notices and signs like "Mixed Cardboard Only" on a recycling bin. Reminds me of a joke postcard I've seen, with a photo of an almost naked woman gripping a racket and reaching to hit a tennis ball, beneath a sign that reads "Tennis Shoes Only to Be Worn on Court." In fact, it reminds me of countless bizarre signs. What were they thinking? I get it now.