If they would have asked me in advance, I would have suggested some sort of LED solution. Heck, for the amount of money they paid for a actual neon sign, they probably could have gotten a blown glass tube in the proper shape and strung a bunch of mini LED's inside of it. Retro-Cool with modern technology.
LEDs aren't always the solution. I had one venue with LED front lighting that would cause havoc with any single coil pickup devices. If the guitar player faced the lights, buzz. If he turned his back to the lights, it was fine. It wasn't a ground loop issue, as the buzz was still there even running wirelessly. The problem was mitigated to a slight degree by putting a steel screen in front of the LED lights. The LEDs were finally replaced, and now the problem has pretty much been eliminated. Totally crazy.