Waaaay back when Spirit and Opportunity landed on Mars in January 2004, the Planetary Society helped the public participate in the missions with a number of projects, including one where we printed "secret codes" around the edges of the two names-bearing DVDs that were bolted to the Mars Exploration Rover landers.
Spirit hasn't talked to Earth since March 22 -- so what new information could they have received that would make them pronounce Spirit's possible death? Is there some new analysis of the last bit of telemetry? Some new model indicating Spirit's survival was less likely than previously thought?
Spirit had been communicating on a once-per-week schedule in recent weeks. During the designated time for the rover to communicate with NASA's Mars Odyssey orbiter passing overhead on March 30, Odyssey heard nothing from the rover.