SAN FRANCISCO (CBS SF)  — It’s called a “warrant canary” and its absence from Reddit’s latest annual transparency report has sparked concern.

The warrant canary isn’t a type of bird. Rather, it lets a service provider inform the public that it hasn’t been served with a secret government subpoena.

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The warrant canary was absent from the San Francisco tech company’s 2015 annual report on government data requests, released on Thursday, leading many to believe that the government may have sent a National Security Letter to Reddit requesting the site hand over its user information — and keep quiet about it.

This annual transparency report is popular among tech companies such as Twitter, Google and Facebook and is used to communicate with its users about requests it receives regarding user information.

Electronic Frontier Foundation (EFF), a non-profit digital rights group based in San Francisco, has described their concerns with National Security Letters on their website, stating:

“Of all the dangerous government surveillance powers that were expanded by the USA PATRIOT Act the National Security Letter (NSL) power under 18 U.S.C. § 2709 as expanded by PATRIOT Section 505 is one of the most frightening and invasive. These letters served on communications service providers like phone companies and ISPs allow the FBI to secretly demand data about ordinary American citizens’ private communications and Internet activity without any meaningful oversight or prior judicial review. Recipients of NSLs are subject to a gag order that forbids them from ever revealing the letters’ existence to their coworkers to their friends or even to their family members much less the public.”

The EFF also states that the “FBI’s systemic abuse of this power has been documented both by a Department Of Justice investigation and in documents obtained by EFF through a Freedom of Information Act request.”

Reddit’s 2014 transparency report states under the section national security requests that:

“As of January 29, 2015, reddit has never received a National Security Letter, an order under the Foreign Intelligence Surveillance Act, or any other classified request for user information. If we ever receive such a request, we would seek to let the public know it existed.”

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Now, in Reddit’s transparency report for 2015, that entire section is missing; the warrant canary is missing.

Reddit administrator and CEO Steve Huffman, Reddit username “spez,” in a thread discussing the whereabouts of the warrant canary said, “I’ve been advised not to say anything one way or the other.”

Later in the online conversation with Reddit users, Huffman adds, “Even with the canaries, we’re treading a fine line. The whole thing is icky…”

Huffman said in the thread announcing the new report that, “In 2016, we’ve taken further steps to protect the privacy of our users. We joined our industry peers in an amicus brief supporting Twitter, detailing our desire to be honest about the national security requests for removal of content and the disclosure of user account information.”

The FBI website provides the public with a template of a National Security Letter, but not much other information.

The American Civil Liberties Union states on their website that they’ve challenged the National Security Letter provision of the Patriot Act in court in three cases and claim the provision “radically expanded the FBI’s authority to demand personal customer records from Internet Service Providers, financial institutions and credit companies without prior court approval.”

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By Hannah Albarazi – Follow her on Twitter: @hannahalbarazi.