One sign I've seen near two airports (most recently outside CLE, the other was somewhere in Maryland) is "Caution - Low Flying Aircraft". As a motorist, what am I supposed to do with this information?

Duck?

Put up the top on my convertable?

Swerve wildly to avoid the oncoming aircraft?

I guess it's there precisely to stop people from doing exactly that last thing, but it was certainly pretty funny (maybe just to me) the first time I saw it.