This, of course, has a profound impact on interstate commerce, and is therefor within the purview of Congress.
New York City spans two different states (New York and Connecticut), and roads are the transportation network that bring things from one state to the next. Honestly, I can't think of a more cut-and-dried case of interstate commerce than this.
Street signs have nothing to do with actual interstate commerce. The Commerce Clause was not meant to apply to things that
might effect interstate commerce, like education.
Seems like a pretty good economic stimulus measure waste of money to me.
Fix'd