Also in the wiki (only relevant for the US, but that’s where Marlinspike is from and likely talking about):

That said, case law specific to the United States would render the covert continuance of warrant canaries subject to constitutionality challenges. West Virginia State Board of Education v. Barnette and Wooley v. Maynard held that the Free Speech Clause prohibits compelling someone to speak against one’s wishes; this can easily be extended to prevent someone from being compelled to lie. New York Times Co. v. United States protects someone publishing government information, even if it is against the wishes of the government, except under grave and exceptional circumstances previously set by act and precedent. This may also have implications in regards to acting against a direct government intervention, similar to a government intervention against a warrant canary.

It’s not illegal (yet), so as long as you’re willing to fight an order to leave it up, you can ensure that your warrant canary is still effective. Either you take it down with no consequences, or you take it down, get arrested, and create case law.

Now, I wouldn’t trust most people or companies with a warrant canary to be willing to do that, but I’d probably trust a wc from Cory Doctorow, for example.