This late addition is courtesy of some brainstorming on the Railwire. This was an interesting suggestion made by Cody Fisher: the shop owner flips the sign over between Open and Closed. The sign is accurately-scaled, so it's only about ⅛-inch wide, so it numbers among the tiniest objects I've animated.
Introducing the beating heart of this project, yet another low-RPM geared mechanism. The small pinion gear, just above center far right, controls the sign's movements. Right above the gear is a microswitch that controls when to stop turning. That tiny hole in the center of the small copper bar holds one end of a 0.004" stainless steel wire; on the other end is the sign. It took a bit of experimenting to render readable signs at that size, and I also tried various colors (fine-point Sharpie); I chose orange, bottom right.
The whole shebang is held in place with one screw (below, lower left), and can easily be removed for maintenance. It's also operated by a single pushbutton: just push it to change the sign.
It's pretty crazy to see the thing in action...
