what does circle with lines on side mean on dash

[latitude500]

So I'm off to have my car inspected today, and sure enough I look down at the cluster and see that one of the displays is lighted up. It's the circle with the lines come off it, looks like a sun. I swear I thought it meant that one of my light bulbs was out. But no it can't be, because it only flickers on when I go over a bump and put my foot on the brake pedal. I checked all the lights and they are working fine.

So what is could it be. Drive me crazy.