I have an idea that could replace flags, signs, blinking and spinning lights, and whatnot. Here goes:
An infrared camera mounted to the A/V scaffolding above the paying field would detect an IR beacon mounted on each of the 6 robots. This beacon would connect to each robot's RC and would transmit team number and alliance information to the IR camera, which would then send streaming video to a computer. Special software (as yet undeveloped) would interpret the video feed, extract the transmitted data, and send instructions to one or more laser show projectors also mounted to the A/V scaffolding. These instructions would include the location of each robot and the color of the alliance each robot was on. The laser(s) would simultaneously light up a circular area on the floor of the arena around each robot in the color specified by the instructions received by the computer. For members of the audience, it would appear that each robot were being bathed in a pool of light in the color of their alliance.
This, sans the exclamation mark (and big ugly ogre), is what I'm talking about
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You could do a whole lot more with this system. Say, for example, one of the robots on the blue alliance has a 'yellow flag'. Instead of a circle of blue light around the robot, the laser could inscribe a spiky blue star around it. Or maybe a robot on the red alliance has just scored 20 points -- the projector could animate the circle for a few seconds, transforming the pool of red light into a rapidly changing mix of shapes. During autonomous mode, all of the pools of light could transform into spinning saw blades. Or maybe at the very end of the match, the projector could simulate red and blue explosions around each robot.
The only problem I can foresee about this system (besides the fact that it would be exorbitantly expensive, would be difficult to set up and operate, and mostly relies on finicky emerging technologies) is that it might be a little annoying to watch. But it would be so cool!