Traffic Calmed Area.

These signs are all over the city.
I find them a bit amusing, silly and a baffling.

What does it mean? Who makes these words up for signs?

Could it mean, 'no road rage ahead!, but no it's for speed bumps!
Would it not have been better to say, 'speed bumps ahead'?

Is it just Edinburgh that has them or are there other cities out there?