So far I have only ever had that light come on due to a dodgy sensor switch. I've had a couple do that, on one the switch actually started spraying oil out of the top too. At least it made diagnosis easy. You can hear on the cb550 when the oil supply to the head is poor, rattles like a can of old bolts being shaken up. Inexperienced owners might not spot it, if the bike arrived sounding that rough like my k3 oil slick did, but once your used to a decent sohc motor running nicely with a civilised exhaust it's fairly clear from the engine note that all is not well pretty soon. Trouble is I like my un civilised exhausts.....
