This isn't necessarily true. I live and work in DC, often as a contractor for the government, including these agencies from time to time. As far as I can tell,

This isn't necessarily true. I live and work in DC, often as a contractor for the government, including these agencies from time to time. As far as I can tell, those working for FBI, DIA, NSA, NGA, NRO, etc. don't have to hide their employer, though they wouldn't disclose it unless they know you. OTOH, I have never met anyone who has admitted to working for the CIA - either directly or as a contractor. There is a definitely a non-disclose policy for them.