Well, canaries ought to be signed with GnuPG or whatever. But then, we're back to https://xkcd.com/538/ ;) But that would be harder against a corporation.
Hypothetically, what would happen if somebody made them use their force in a very public, visible way (that is, refuse to comply, and post live video on multiple video sites)? How big of an operation can be kept secret by physical violence?
There wouldn't be some sort of black-ops, Bruce Willis style operation. You'd simply be someone being arrested by some FBI agents for violating federal law, and they could do that at noon on a Tuesday smiling to TV cameras if they wanted to.