Or it could just be hacked; there are plenty of examples. These signs are (usually?) programmed via a cellphone, and apparently many townships leave the passcode as the default, which can be found online.
Nice. An old ASR-33 or IBM Selectric would be fun to modify, as well. Or learn Morse and use an old telegraph sounder. http://steampunkworkshop.com/images/fl-12.jpg An Arduino could easily do the conversion.
We were told they could eat as much as they wanted, but were punished if they left any food on their plate. Overfed prisoners are easier to control, I guess.
I've seen pool players use them as well. And a friend has a sheet of micro-prisms attached to one side of his eyeglasses to correct for a vision misalignment.