In message , at 12:33:13 on Sat, 9 Jun 2007, Andy
Hall remarked:
- The piece of paper is too small to be read on a moving vehicle
either by eye or by camera
They are colour coded sufficiently that grossly out of date discs
can be easily spotted from a distance.

... and this happens how frequently?

I have no idea how often this visual clue is the trigger for a more
exhaustive investigation. But it's undeniable that the clue is more
obvious to an observer than the expiry date.
--
Roland Perry