It means that there is something wrong with your suspension system. It has a code stored in memory, the definition of that code will point you in the right direction for fixing the problem.
Press the "OFF" and warmer (red) buttons at the same time for about 5 seconds and the whole dash board will light up and start displaying codes. Any codes that are in the format of "S###" is a code that pertains to the RSS. They will come up either as "HISTORY" or "CURRENT", history just means that it was a problem encountered in one of the last 50 startups, and current means that it is a problem that is currently happening on this startup. You have to keep in mind that it can only test most of the suspension components while the car is moving, so the codes will always be displayed as history unless you went for a drive and then checked the codes before you turned the car off. Current RSS codes are what put the SRC light up on your dashboard. To exit diagnostics mode just simply turn the key to the off position.