Up until recently (18-30 months ago) NSA employees were only allowed to identify themselves as employees of DoD. It was common knowledge, that unspecific references to Fort Meade meant NSA; and if you saw a P.O. from Procurement Office, Fort Meade, it meant the NSA was buying it.
Nothing has really changed. During orientation, you are told to keep your NSA affiliation low key. But you are not ordered to. This was part of the No Such Agency stuff, trying not to draw attention to yourself or the Agency, and to avoid questions from the curious. Perhaps the most important reason for keeping it low key though, was to preserve your career options. But for disciplines such as crypto, the choices are quite limited so broadcasting you are NSA does not matter much.