Daft idea's.

[ppppenguin]

A better solution would be red and green, a pretty universal indication of stop and go.

Lots of red/green colour bllind people. OK for traffic lights where by convention red is at the top. Unless you know any countries where this isn't so.

Terry, I think you're right about Scheveningen, but Schipol and a number of other places would have been just as good at distinguishing Germans from Dutch. The whole thing may be urban myth but it's good story.