This is somewhat crazy, but it would work if you can't find your car in the parking lot.
So you would attach a device on the top of your car that would shoot out fireworks when you pressed the button on your remote control. Not Times Square New Years eve fireworks, mind you, but just a mini harmless one. I understand the authorities may frown on it, but can we please make one little exception here?
IF it's totally verboten though, let's use those green lasers in conjunction with a cloud of mist or smoke that is spewed out of the top of a car.
Reward: Hmmm, I'd like a digital camera: just the average Kodak. And some tootsie-rolls.