Saw a news article from yesterday discussing the TSA's interest in using an electronic randomizer to randomly assign passengers to checkpoint security lanes.
The idea that they need to get proposals on whole systems to do this. They're really overthinking the problem here. They don't want any sort of indication of positive negative, for example the colors red or green. I'm not sure why they want to assign a binary result, anyway. Do they think airports only have two security lanes?
All you need to do is assign each checkpoint a number, and write a really simple program to randomly choose a number and display it. Here's my web-based implementation. It shouldn't be terribly difficult to write an iOS version and send out iPod Touches to airports to run it.