If you plan to fly in the Washington, D.C. area, there will be a new visual warning system in use beginning May 21, as explained by this information from the FAA:
Subject: New Visual Warning System for restricted airspace around Washington, D.C.
The Visual Warning System (VWS) is designed to warn pilots who have entered the Air Defense Identification Zone (ADIZ) over the Washington, D.C. area without the authorization of Federal Aviation Administration (FAA) Air Traffic Control. VWS is a ground-based system that uses safety-tested low-level beams of alternating red and green lights to alert pilots that they are flying without approval in designated, restricted airspace. These visually conspicuous lights, distinct from other light signals currently used by FAA Air Traffic Control, are designed to provide a clear warning to pilots who enter the ADIZ without authorization and cannot be contacted on the radio by Air Traffic Control. The VWS will become operational in the Washington DC area on May 21, 2005.
For more information on VWS go to:
http://www.faa.gov/news/news_home/visual_warning/
http://www.norad.mil/index.cfm?fuseaction=home.news_fact_vws
Jan Hoynacki, Executive Director
United States Pilots Association