[TheLoneAdmin]

The government can issue a gag order on a specific subject. This prevents you from disclosing the existence of a subpoena. However, the opposite is not true. The government cannot compel speech.

Sure, the government can take illegal actions...

However, they cannot force someone to make an untrue statement.

[zaarn]

Maybe they can't force you but you might still be found in contempt of court and jailed or fined large amounts of money.

Either option, force or contempt of court, isn't that well explored in the domain of cyber security yet, especially because the lack of updates on the warrant canaries are supposed to communicate something and the lack of updates would therefore also constitute communicating the presence of a warrant to outside parties.

Law isn't like logic puzzles.