Uh, why should the lifespan of a roadsign be only ten years? Unless they're really, really shoddily manufactured?
It could be that the printing of the name on the background takes a beating and the letters either darken or peel off.
Their deadline is two years less (20%) than the average longevity of a street sign. That hardly makes it a case of replacing the signs as would be normal.
...But many street signs would already be nearing replacement.
FWIW, there are still street signs around here for the City of Port Melbourne, which means at least 15 years old.
