growing on the warning you are entering a unauthorised area thing, why not something like this ' WARNING THIS AREA IS QUARRENTINED DUE TO A MINOR RADIATION LEAK. IF YA DONT HAVE ANY KIDS YOUD BE BETTER OFF BACK HOME WITH THE WIFE/GIRLFRIEND THAN HANGING AROUND THIS CAR LOT.' you could still add the machine gun fire for added drama, maybe add a few automatically set off smoke bombs, oh,,,,,,and a few flashing lites.
