I remember an email conversation I had with a ready-mixed concrete company, some 5 years ago.
I had seen one of their lorries, in Sheffield, which had one of those signs on. Trouble was that it was something like 12' up in the air! Hardly easily noticeable by cyclists.
I have seen, recently, more whereby the sign is lower down, in the eyeline of cyclists, and drivers. Maybe the signs have always been there, just not noticeable until moved further down?