See if that was actually a standard for driving, I'd understand.
But we have billboards, decorations, floppy men, people dancing on the side of the roads.
If all that is allowed, I can't really be offended by a sign saying "don't kill people" as a form of protest.
I mean, if we care about confused and distracted drivers I have a LONG list of things I would put over caring about before this.
An extra street sign wouldn't register on my worry list.