Much more likely to mentally skip over an extant negation than introduce a phantom one. My personal favorite: Driving through backroads with some friends, sign

Much more likely to mentally skip over an extant negation than introduce a phantom one. My personal favorite: Driving through backroads with some friends, sign says "Impassible Road: No Tow Service Available". Friend turns down it, drives half a mile, gets stuck. "No worries, we'll just call the tow service. Anyone remember their number?". Queue a half hour of us on our knees digging mud around.