Thermo said:no it wouldnt be legal under the construction and use regulations of the road traffic act
Ah, but is it strictly an infringement? After all, displaying red lights at the rear of the car is within the rules. As is displaying signage (unless you want to stop every tradesman and bumper-sticker owner in the land). So surely combining the two would not be illegal?
Sure, occasionally a policeman may stop you and remind you that it is irresponsible because you might upset some irate road-rager with it. They might even give you a producer, but what is the law that disallows it?
I often wish I could press a button and have the message "What is in my boot that is so interesting that you have to sit 3 feet from my back bumper?" or "Wow, my eyes must be good to see so well in this thick fog that has made you turn your foglamps on!". Or even just the word "To**er" for those really 'special' drivers.