http://www.jpl.nasa.gov/releases/2004/29.cfm
"Spirit rover communicated with Earth in a signal detected by NASA's Deep Space Network antenna complex near Madrid, Spain, at 12:34 Universal Time (4:34 a.m. PST) this morning.
"The signal lasted for 10 minutes at a data rate of 10 bits per second.
"Mission controllers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., plan to send commands to Spirit seeking additional data from the spacecraft during the subsequent few hours. "
Probably the safe mode is by design. If commands are effective it will return to the normal mode.