[mseebach]

Moxie Marlinspike: If it's illegal to advertise that you've received a court order of some kind, it's illegal to intentionally and knowingly take any action that has the effect of advertising the receipt of that order. A judge can't force you to do anything, but every lawyer I've spoken to has indicated that having a "canary" you remove or choose not to update would likely have the same legal consequences as simply posting something that explicitly says you've received something.

https://github.com/WhisperSystems/whispersystems.org/issues/...

Bruce Schneier: Personally, I have never believed this trick would work. It relies on the fact that a prohibition against speaking doesn't prevent someone from not speaking. But courts generally aren't impressed by this sort of thing, and I can easily imagine a secret warrant that includes a prohibition against triggering the warrant canary. And for all I know, there are right now secret legal proceedings on this very issue.

https://www.schneier.com/blog/archives/2015/03/australia_out...

At the very least, the issue isn't clear-cut, and there most certainly isn't constitutional precedent.