I think it would be cool for the Volt to have a lighted Volt logo on the back when the car is in EV only mode. The car would be bragging to all of the other cars that it is in EV mode and not currently consuming any gas.
I know this requires some electricity but a single LED on the rear trunk illuminating a little lightening bolt would be cool. It would tell the world and all of the other drivers that you just passed them without using gas! It would also help separate the Volt from the wanna-bees like the Prius. What do you think?