Coming out of London City Airport the other day, I was intrigued by two large signs instructing pilots to "CAUTION YOUR BLAST". Obviously this was the first thing I typed into Google when I got home, and it brought up many webpages with people asking what it meant. The answer I like best is the one that says it means not to accelerate too rapidly going onto the runway because you run the risk of blowing the ground crew over in the process.
(rab) How do you caution a blast? Do you say "OK, blast, you've committed an offence but we've decided not to prosecute this time provided you admit culpability"? Why don't these buggers speak English?
I think it might be due to limited sign space. I trust the interpretation of the message is part of a pilot's training, as being a native English speaker won't even help you with this one.
[rab] The turning points at LCY are very tight, and I suppose it must be to remind pilots to be wary of where their blast is directed. This video shows an example of people not cautioning the blast of a Airbus 340, where the pilot has no choice of where to direct his full throttle "blast".
It'd be interesting to collect signs that don't entirely say what they mean. The only two I can think of are "Blind Summit" in the UK, which means "there's something you need to be ready for beyond the crest of this hill; such as a single-track bridge, an abrupt curve or a yak crossing, but we're not telling"; and one you often see when exiting tunnels in the US, which just says "Lights". It's reminding you that you might have left your headlights on when leaving the tunnel but presumably they don't want to say "Turn your lights off now" for fear people would obey it at night.
(Dan) There was a (maybe apocryphal) example of that at a level crossing in Yorkshire where it said "Wait while red light shows" in case there's another train coming in the opposite direction. But there were cases where motorists stopped at a green light because colloquially the sign means "Wait until the red light shows". There are so many ways of rephrasing it but they missed them all.