Combine the Persistence of Vision LED display with a rotating Fan, when its windy the blade spins. While the blades are spinning they power a microprocessor controlled array of LEDs on the fan blade.
Using a persistence of vision trick a scrolling message can appear when the Fan blades are spinning fast enough.
Colour Animated graphics are also possible with RGB LEDs.
This kind of sign could be nearly any shape or size, so long as it is free to rotate and catches the wind. A certain minimum airspeed is needed to the persistence of vision effect to work however.-- Melchior, Apr 19 2007 Baked Ceiling_20Fan_20TVCeiling Fan TV [trekbody, Apr 19 2007] You could store the electricity generated by charging a battery, and then use it to power the display when the wind isn't blowing.I'm sitting about 20 feet from one right now, so I guess it is baked.-- AbsintheWithoutLeave, Apr 19 2007 random, halfbakery