If you live in the District of Columbia, you've got to register your car. Some people don't do that. So the D.C. police have stepped up enforcement of that law. Parking enforcement officers patrol the streets, looking for cars with out-of-district tags. When they find one, they record the tag number on a computer. If they spot it in the same area again within 30 days, they issue a warning to register the vehicle. If they find it a third time, they can ticket the car or even have it towed. But people who live outside the city say they've been ticketed while visiting friends or taking classes or even just going to nightclubs or restaurants.