Ah yes, the car obsessed maniacs who exist to drive cars badly. But everyone needs a purpose in life, so is it fair to be cruel?
This RTA video is very good, and depicts a rather sad but all too frequently encountered scene.
You really will have to watch it, and if cyclists and the responsible 'other' road users adopted the sign universally it would be quite an effective example of road-user solidarity.
Judge for yourself and watch this little beauty: