I saw this on a truck (non UK plates), and they do puzzle me a bit.
For a start, it is not clear - are the black bits the death angles - in which case why the big black areas in front left and right where there is clear diver visibility? Or is it the yellow bits with the warning triangles, in which case why the bits left and right which are also clear driver visibility. It makes no sense!
But the bigger issue is how we seem to find it quite acceptable to allow death machines to be driven on the public roads like this. I mean that is what it is saying - angles mort - death angles - places where you could die even though you might be a legitimate road user legitimately in such a place on the road.
Surely if there is a dangerous machine, a machine that can kill people, we need to make it safer, including mirrors or even cameras if necessary, and driver training, to ensure there are no "death angles".
To be honest this seems a lot like victim blaming.