Seth Godin points out a type of sign which has been annoying me whenever I see it, for exactly the same reasons:
Leaving aside the obvious contradiction of strategy (laptop users are more likely to buy books and less likely to steal stuff, so why not let them in the store and offer them a mesh [...]
Last night I made an order on Amazon.co.uk [my wishlist, it's worth a shot!], I didn’t need it in a hurry and so merged it with a larger order which is due at the end of september in order to save on the postage costs.
I got the "merge done" screen, but not the emails and [...]
Signs to Customers