its a warning light to say you have a bulb out. with mine it was a rear side light out.
it happened again the other day and it was a brake light bulb out this time.
the light came on in the morning and went out by the time i got to work, when i checked the lights at work they were fine, on the way home it came on again and stayed on, i checked the lights and the the offside brake light was out.
so basically if there is a bulb or light issue this warning light appears.
Ian.