The Sinewinder lighting is powered from the receiver, and is not connected directly to the main battery supply therefore I would say it doesn't reliably indicate if the robot is powered up. You can also control it from your transmitter (i.e. turn it on or off) and while you wouldn't really need to turn it off, if it does get turned off, it could lead people to believe that your robot is not live, when it actually is. I had a Sinewinder on Drumroll at a competition once and it kept cutting out mid-battle, so not a good indication of the robot's power state!

My advice would be to buy a proper LED such as: http://www.technobotsonline.com/led-24v ... inent.html

which would be connected to your main batteries and then have the Sinewinder connected to your receiver purely for the 'fancy' factor. The proper LED will be a lot brighter so should be more noticeable as an indicator of the power state of your robot, but just make sure at an event that the arena marshals are aware of what light represents what.

EDIT: What Terry said