I get the impression that you've asked this question but, following your reaction to plenty who have now posted what they reckon, you aren't really that interested.
Nah, I can disagree?
I reckon apart from everything else, if you put a warning sign on everything, it becomes commonplace and loses its impact.
I thought these signs were introduced due to the problem caused not by rear visibility, but by cyclists disappearing into a nearside blind spot? Otherwise why not have them on both sides? As Gavintc said the nearside is well covered by the mirror. I took note on this mornings walk, at the side of the cab the window begins at rib level - I should be just as visible to the driver as if he was in any other vehicle.
Theres no nearside blind spot for something the size of a cyclist, unless on a recumbent.
I'd like to see more of these warnings. On wagons and busses.