"Grounding ballasts and luminaires is also important to ensure the proper starting of the fluorescent lamp, especially when working with magnetic ballasts. A metal reflector creates a capacitive path to ground through the wall of the fluorescent tube, which aids in ionizing the tube?s gases and triggers conduction. Once the tube has started, the supplementary capacitance becomes obsolete because the impedance in the ballast circuit is actually lower than this capacitive path."
On horseshoe fluroescents they often run a foil strip along the tube for grounding purposes. I could see an issue with signage where there's no nearby ground plane since the tubes often span open air.
