https://gigaom.com/2014/09/18/apples-warrant-canary-disappears-suggesting-new-patriot-act-demands/
Apple included language in its first Transparency Report to say that it had not been subject to a Section 215 Patriot Act request. That language is now gone.
The canary is an indicator of two things: Apple's attitude about these types of data demands, but also the terms of the court settlement that finally allowed the companies to disclose their compliance wth even secret requests. It is my understanding any such "canaries" had to be removed in favor of the reporting of ranges of surveillance requests.
From your linked article:
"Update 2: Ars Technica suggests that the disappearance of the warrant canary is a result of Apple following new Justice Department guidelines that permit companies to immediately publish ranges of surveillance requests — so long as the figure reflects a combined number of FISA requests and NSL requests. In other words, Apple may have received NSL requests, but not FISA ones (that does not necessarily explain, however, its decision to remove the section 215 language).
Apple, in those last two Transparency Reports since the court order allowing the comany to report the number of Surveillance Requests, has reported they've received in the range of "0 - 249 requests". Note, that still includes zero as a number. However, even if they receive a request, without your private key, such a request will return not much more than the proverbial name, rank, and serial number, and a gigabytes of 128 bit indecipherable gobbledegook.