From: Cathal Garvey <cathalgarvey@cathalgarvey.me>
The question is not whether or not you can securely disclose that you are under NSL. The question is whether you can do so without, when the word breaks, being in trouble for leaking that information. So yes, you can establish all sorts of wonderful contraptions that "get the word out", publicly or privately, on or off-shore, so that the people outside can disseminate warnings that you've been compromised. But in the end, the stasi will blame you, and no matter how much cooked-up legal convolution you wrap yourself in, they will nail you to a cross.
Generally, legally agents of a corporation cannot conspire with each other. (Google: 'corporation cannot conspire with itself' https://www.google.com/#q=corporation+cannot+conspire+with+itself ) Therefore, one possible tactic for a corporation that receives an NSL is to deliver a copy of that NSL letter to each of its employees, including employees of all subsidiaries, naturally with a stern letter that they not disclose that to anyone else! Obviously, that news will leak. The government will 'know' that somebody, probably within the corporation, did the leak. But given the size of the typical telecommunications company (thousands of employees), the actual source(s) of the leak(s) will be unknown. Prosecution of any specific corporate employee will be difficult without very detailed evidence. The issue will arise: Can a corporation legally deliver a copy of that NSL to each employee? Well, each employee would probably be 'imputed' (legally assumed) to know of such an order, even if they did not actually know of it. Since they are legally obliged to comply with that order, it would be grotesque to not allow them to become actually aware of that specific order. I think in the end the courts would have to agree that a corporation is entitled to inform each of their employees of the existence and content of the NSL. Jim Bell