SpiderOak says you'll know it's secure because a little bird told you
Edward Snowden–endorsed cloud storage provider SpiderOak has added an additional safeguard to ensure that its users' data doesn't fall into the hands of law enforcement without their knowledge, in the form of a "warrant canary."
The term takes its inspiration from the practice of bringing actual canaries into coal mines that could potentially be filled with invisible noxious gases. If the bird drops off its perch, you know something's wrong.
Similarly, a warrant canary is a device that's designed to let you know that something has gone wrong with an online service, even when there are no obvious signs of trouble. In this case, "trouble" means the service provider has been ordered by a court to turn over user data, but a gag order prevents it from disclosing that fact.
