What kind of activity should I look for?

You should immediately report people who photograph, videotape, sketch, ask detailed questions about or seek blueprints for: airports, water supplies, dams, bridges, major highway intersections, tunnels; power plants and substations, transmission towers; pipelines and tank farms; military installations, law enforcement agencies and defense contract sites; hospitals and health research facilities; internet, phone, cable and communications facilities or towers; and capitol, court and government buildings. Suspicious activity around historic structures and national landmarks should also be reported.