In defense of the "obvious" sign
Now I support the PEC and their activities to encourage the use of using plain language in official communications and any other "functional" communications, but in this case I am not so sure they are right. Many of the examples they give are merely signs ensuring compliance with legislation. If the law says that all products containing any trace of nuts must be labelled "May contain nuts" then a package of nuts must also be labelled in the same way, idiotic though it may look.
But one example they give is even more interesting. They seem to find very amusing the sign "Caution: water on road during rain". But this is actually the symptom of another problem. The sign could perhaps be worded better, but to me the meaning is clear. On a normal road the surface is convex so that rain runs away. But if there is a defect in the road surface then sometimes after rain some water can remain on the surface. This is what the sign is about.
In this case I think that the problem is not the sign but the road. If the road is in such a state that the water stays then the solution is to fix the road, not put up a sign. I can understand a temporary cardboard sign erected when the problem is noted, but not a permanent installation. This, however, reflects a certain mentality that thinks a sign is a solution. In fact in an ideal world the sign should not be needed.