This week's New Scientist (August 29 - September 3, 2010) notes a road condition disclaimer usage that I too have been amused by: "Icy conditions may exist". Way to take a firm position there, Department of Highways!
It reminds me of my favorite "lost or stolen item" disclaimer, on a coat check rack in a place I no longer remember: "Not responsible for personal loss."
Obviously, these are the result of too-creative responses to the problem of having a warning sign that may or may not be relevant to the actual situation. Warn of ice in July? List all the things your patrons may lose or have stolen? It's fear of sounding dumb, which leads to sounding even dumber.
For example, consider the problem of the exit from a long tunnel, where people have put on their headlights. It may or may not be daylight on the far side. Do you tell them to turn off their headlights only if it isn't dark? The solution, I've read, is just one word: "Lights?" Leave it up to the user.
At work, in the bathroom, is an insultingly detailed discussion of why I should wash my hands after using the toilet. Now, I appreciate that this is a real hygiene issue: a physician acquaintance once told me of observers at an infectious disease conference who were startled by how few of the participating physicians washed their hands after using the toilet. If you want to know how smart doctors really are, just watch their behavior when they aren't pushing you around or giving you useless drugs... On the other hand, don't. It will just make that health insurance bill even more unbearable.
But as for the sign at my work bathroom: I'll bet the level of compliance is lower than if the sign just said "Hands washed?" Appeal to my sense of self, not some alleged rational faculty I barely possess, and that I certainly won't activate on your account.
But what communications department is going to leave their work at two words? Makes you look lazy. "How much did I end up paying you per word?" So you create a big illustrated poster with a bunch of useless text whose only effect will be irritation. Believe me: this is my life.
At least my work life.