This is a way cool idea. I hope someone here gives you a hand with this. It can't be that hard. I'll bet you could do it with a relay and a hacked remote control.
My Tivo has an LED on it the blinks whenever you press a key on the remote so you can tell it is receiving the command from the remote. All you'd have to do is hack something similar and put the LED in your helmet.
[Edit] - Here's an article on how to build a remote control LED light. You wouldn't need the plug in power supply, just use AAA batteries instead.