If they can deny you access to the info because of national security, then "still a sign that they have info" is a solved problem. They "can neither confirm nor

If they can deny you access to the info because of national security, then "still a sign that they have info" is a solved problem. They "can neither confirm nor deny any the existence of any information matching your request." This is known as the "Glomar response" and dates back to the 1970s. I believe it hinges on "if the information existed it would be classified," otherwise they would be required to provide the info. https://en.wikipedia.org/wiki/Glomar_response https://en.wikipedia.org/wiki/Glomar_response