OK, what if you provided total read-only access, to everything on all of your machines, networks, communications and so on, to someone like me. Someone who you could trust 100%. And whose reputation depended on that. Someone who was totally anonymous (which I'm not, but I could have another persona that was). And someone with such deep backdoors into your stuff that they couldn't be evicted.

And so it's that person who maintains the warrant canary.

Or instead, it could be an ~undocumented feature of your outside counsel. Because you do have the right to outside counsel, I think, even regarding NSLs.

Edit: For example http://www.cryptohippie.net/AnonAdmin.html