The US government has the power to issue people with what are known as ‘national security letters’ that require recipients to not only give the government any data it requests even if it is about their clients, but they are forbidden to tell anyone, even their lawyers, that they received such a letter. So for example, they can ask your librarian to tell them what items you check out or your internet provider to hand over any information they have on you. It is an astounding assertion of government power and shows the reach of the national security state.
One way to circumvent this gag law is to create a ‘warrant canary’. Although it is illegal for the recipient of such a letter to say that they received such a letter, it is not illegal to say that they did not receive such a letter. So some companies have taken the route of having a statement on their website stating that they did not receive such a letter. If they remove that statement, that means that the so-called ‘warrant canary’ has died and is an implicit statement that a letter was received.
It appears that Apple’s warrant canary has died (i.e., the statement has disappeared) suggesting that they have received something from the government that prevents them from continuing to provide the assurance.