Actually there is a federal law that can ban this whole entire forum then if you look at it that way..
DOT law says that anyone is to; "in no way shape or form to modifiy, remove or replace "vehicle standard" equipment on a vehicle. Vehicle has to be modified/replaced or repaired by only a certified and registered DMV shop, or DOT station. DOT and local authority has a right to inspect the repair or replacement or modification and is to approve it before vehicle is to join public highway traffic...."
Technically, cops can give you a ticket for violating DOT laws cuz your "aftermarket" wing has no "DOT and number" printed on it. Or your ricer rearview mirror. Same for the radio, any part of the engine or whatever else has not been specifically approved for highway use and stamped with DOT numbers on it.
Like.. let's say for argument's sake you manufacture your own TIRES. Or glass. Or antennae. If you don't have a D.O.T. number on it = illegal = not approved by highway use = ticket. Aftermarket auto market knows this, that's why a lot of them are trying to get themselves a DOT inspection and approval on the product they sell or manufacture.
Do Neon lights under your car have a "DOT mark and number?" No. That means that manufacturer of those neons has NOT gotten a permission to INSTALL this on a highway vehicle. Does that stop them from selling it? No, law says nothing about that they can't sell it. Just look at your headlight lens, it has a DOT mark, so does a bumper, door, tire and even glass.
If it ends up on your car, it's your responsibility. So is the "Dr. Dre" CD hanging off your mirror. Here in NY, they call that "an obstruction of driver view." Big loud exhaust? OK, prove in court with a picture and a signature from a DMV local repair shop that it has DOT markings on it and it passes emissions, and then you can use it. Tinted windows here are "dangerous visibility decrease." They actually have cops on street corners with "light guns" to check your tint, anything more than 10% is immediate tow and ticket. Believe it or not, they had decibel meters as well awhile ago, i dunno if they still do that, haven't seen it in a while.
Personally, I don't mind seeing neon lights under car. Some look good, some look as if you have a floorboard missing and your car is a POS. Smoking ban in bars and clubs is bullshit. So is law against seeing tits on public TV. I think they are all bullshit laws.
If you like neon, use it. But you will have to convince your Congressman/woman to change that law, not me.