From the looks of it, some guy was really annoyed with getting up from his office desk and walking all the way to the bathroom, only to find it occupied. It's a common problem to be sure. But most of us don't have the ability to hack together a device to alert you on your computer screen when the bathroom is available (the green alert light on the status bar):
To solve this problem, I took a Make Controller from MakingThings.com, wired a couple of Vishay TEMT6000 ambient light sensors (photo transistors) to it, then wrote a Mac desktop app to sit in the status bar to show everyone the status of the pottis. I call it, "iPotti™" and it works awesome!
At the heart of iPotti™ is the Make Controller. It's an Atmel Sam7 ARM microcontroller with the Make Interface Board stuck to it. The Interface Board has Ethernet, USB, power and breakout headers for the pins of the microcontroller. I wrote a slim little piece of firmware for it that simply broadcasts UDP packets with the status of the pottis. It broadcasts a packet about every couple of seconds.