Its an interesting question whether the FAA would initiate or participate in any challenge to the LA law. The FAA would likely have automatic standing to challenge the law in federal court on grounds of preemption. They have done it many times before and often won. One time they lost big though was when they challenged a local Hawaii law which prohibited airplanes from towing advertising banners in the sky. The concern was that such aerial activity distracted drivers on the roads below creating a risk to public safety. The FAA argued that they regulate the airspace in Hawaii and everything in it and were alone authorized to decide what aircraft could or could not do while flying through it.
The Federal Court of Appeals ruled that state and local governments have the "police power" to protect the health and welfare of their residents and if they say no to sky signs, then that is how its going to be. This is an example of how application of the federal preemption doctrine has limits.
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Could be possible reckless endangerment to do this is some places. Please check LAANC, state and local laws and ordinances and fly and tow responsibly.