A great joke would be to have a short piece of an extension cord hanging out from the rear hatch or somewhere around the license plate. I can imagine the truly concerned comments from people thinking it could electrocute someone. :lol:
Then again it could also confirm peoples belief that the car needs to be plugged in :roll:
Thats likely just a plug in for a 12 volt power supply so lights and other various items can be powered while the car is on display. I've seen this at all sorts of indoor car shows/expos. It's common, especailly when the vehicle has a lot of lights or stereo eqipment to run. They probably had the headlights on or something for the display.