First I would make sure it's bled. Unscrew the plastic screw next to the overflow tank. Crank the car and let it warm up. turn on the heat. Add coolant until coolant comes out of the bleed hole with no bubbles. A little messy, but these cars are notorious for being hard to bleed. that way, if the light comes on again, good possibility you have a leak somewhere.
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.