Years ago, back in the dark days of coal mining a hidden danger lurked - Firedamp -pockets of methane that could be ignited by the miners' lamps which could trigger a coal dust explosion with very nasty results. Caged Canaries were used to alert miners to the presence of firedamp and other toxic or dangerous gases. If the canary showed signs of distress or stopped singing you would double time it out of there.
In this day and age we now have the "Warrant Canary", a method ISPs and others can use to let their customers or audiences know that they have not received a secret subpoena or National Security Letter from the US Government (usually FBI or DoD).
The principle is this: An ISP or organisation periodically makes a statement (usually digitally signed and often including some recent news reports from a well known source) attesting that they have not received any NSLs or secret subpoenas. The theory runs that false speech cannot be legally compelled so the absence of such a notice would notify those watching that there could be a NSL or subpoena in place that has a non-disclosure element to it (a gagging order as it were).
Some organisations include a Warrant Canary in their transparency reports (Apple for example), others have alluded to their use to warn that products or services have been compromised.
Anyhoo, a new website called Canary Watch has been set up to track warrant canaries.
As to who is behind this site? the About section says:
Canarywatch is a coalition of organizations including theElectronic Frontier Foundation, the Berkman Center for Internet and Society, NYU's Technology Law & Policy Clinic, and the Calyx Institute. The Calyx Institute runs and hosts canarywatch.org.
Warrant Canaries so far seem mainly to be a US phenomenon but they are becoming a popular feature of services and applications that value privacy and confidentiality and may not be immediately apparent (TrueCrypt springs to mind).
It's a site worth keeping an eye on. It's early days yet and their Twitter post states they have been overwhelmed with submissions so expect to see a lot more entries.