They're state laws. It's a 9th/10th Amendment issue. A federal billboard ban would certainly seem to violate the 1st.

A ban in California would seem illegal as well, due to the affirmative right to free speech contained in the California Constitution (see Pruneyard Shopping Center v. Robins).

Here in Maine, on-premises signs are allowed but have strict limitations:

https://legislature.maine.gov/statutes/23/title23sec1914.htm...

But the supremacy clause (https://en.wikipedia.org/wiki/Supremacy_Clause) prevents state laws from preempting federal laws, including the constitution.

Yeah, you're right.

It looks like sign bans are usually unconstitutional when content-based, where the substance of what is being communicated is taken into account (e.g. bans on only commercial signs), but generally hold up if content-neutral and based on reasonable factors, such as safety or aesthetics.

See Reed v. Town of Gilbert (content-based ban struck down) versus Scenic Arizona v. City of Phoenix (content-neutral and safety-based ban on electronic signs upheld).

https://www.scenic.org/sign-control/billboard-laws/important...

If the sign throws fireworks at passers-by, yes. Because the point of a billboard ban is not their contents, but the distraction they cause. It would be enough to tune them down and nobody would mind but yeah, losing perceived ad revenue is somehow never the first thought.