"If you can't see my mirrors, I can't see you" is a common warning sign on the back of big trucks — and it bugs me because, in fact, it's so wrong! A trucker can often see a car without the car's driver being able to see the truck's mirrors.

Simple geometric optics — straight-line ray-tracing — suggests the more accurate: "If you can't see my eyes in my mirrors, then I can't see your eyes in my mirrors". Yeah, I admit it — that's far too convoluted for most tailgate-hugging motorists to appreciate or find useful. And it's not the whole story, given the fact that (most) people have two eyes. Plus which, light is a wave and diffracts (a little) around corners.

So the bottom line is, don't ask a physicist to design traffic signage. But meanwhile, maybe a better caveat to post on a big rig is something akin to "If you can't read my mind, I can't read yours" ...

TopicHumor - TopicScience - 2003-06-09

The simple intended meaning If you can't see both my mirrors, you're too close wasn't catchy enough (and still not completely accurate). The obscurely thought is the obscurely formulated, or some such. If you can read this... in small print, is much more accurate, but tends to become self-fullfilling. Was popular around here for a while, years ago, but it increased the incidence of tailgating. – Bo Leuf

(correlates: ForTheVisuallyImpaired, PardonMyFrench, HakoneEkiden, ...)