For those who don't know, a warrant canary is the periodic transmission of a statement along the lines of, "We have not received any warrant demanding your data." If the message stops being sent then the recipient(s) can assume such a warrant has been served. The idea behind this is that the gag-order that often accompanies such demands from law enforcement cannot prevent a person from not speaking.
Until now. In Australia.
Warrant canaries can't be used in this context either. Section 182A of the new law says that a person commits an offense if he or she discloses or uses information about "the existence or non-existence of such a [journalist information] warrant." The penalty upon conviction is two years imprisonment.
In truth the warrant canaries were unlikely to work for long. In the current, fear driven environment there is little reason for law enforcement to restrain itself from coercing the target of a warrant into sending false canary messages. By outlawing even the attempt to use a warrant canary, the Australians are just being more honest about being a bunch of progressive schmucks.
I anticipate similar wording will be added to US law.