That is probably your brake wear warning light. This is for the front brakes, at least it is on my car. I agree that there may be something loose if you're only getting the light when hitting bumps. Check the front brake pads.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section