Threat Advisory warning signs indicate current National Homeland Security (NHS) level of alert. Weather- and sun-resistant signs feature 5 interchangeable panels that correspond to NHS color-coded levels. Panels slide into aluminum track and snap in place to secure against wind and vibration. Bright colors and optional reflective finish increase visibility. Standard main sign measures 14 by 21 ins. Other sizes also available. Ideal for airports, military installations, ports, and public administrative.