I found these electromechanical vane displays on eBay and accidentally won them. So, here they are!
These are seven segment displays. Each segment is painted a bright yellow and fluoresces under UV light. The segments do not actually draw any power except when they are moved. Behind each segment is a solenoid that flips the segment on or off. Several units are then daisy chained together to form larger numbers. Watch the video below to see it in action and be sure to check out the image gallery.
(P.S. Sorry for the heavy Minnesota accent in the video.)
A vane display is a type of 7-segment display. Unlike LED and VFD segmented displays, vane displays are composed of seven physical surfaces, typically painted white, but occasionally other colors, such as yellow or fluorescent green. If a segment is to be displayed as “off”, it will be rotated so that its edge faces forward, with the painted surface pointing away and not visible. A segment that is to be displayed as “on” will be rotated so that the painted surface is shown.
Vane displays operate in a similar manner to flip-disc displays, in that the segments are quickly moved using electromagnets. Some variants used where the display need not necessarily be changed quickly use electric motors to rotate the displays in and out of place.
Learn more about the technology here: http://www.scoretronics.com/
EDIT: You know who rocks? Adafruit.