My pet peeve is this but for signage in general. Workers put out a temporary flood or road narrows sign, but forget to remove it again, the net effect is just people learn to not notice signs as much, and works against safety.

Still regularly see signs about masks obligatory, keep 2 m distance, and one-way systems from covid. They’re just part of the background now, people don’t even see them. And next time they’ll be that much less effective.