More comment here:
until they wipe it.
The real message should go to lorry drivers, what should they do in that situation? Also I agree with Brun's comment about the artic, not only is it less common in London, the poster shows it in an impossible position, at that junction an artic would have to move right out into the junction before turning. The driver should be able to do that in a way which puts all the cyclists in the field of view of his mirrors.