A glowing neon "open" sign, complete with wires and a frame and all that. I don't think it is 100% accurate, as it was based only on reference images found online, but the setup is plausible at a glance.
The neon tubes and translucent clips [emitters] are on layer 1, wires, clips, the frame and bars, etc., are on layers 2 and 3. The lighting and background plane are on layer 5.
Note that the image renders in two passes, one for emitters, and one for everything else, which are mashed together in the compositer.