I've only seen a video of the ACC system being used...and it was by an e38 owner from the Netherlands (Big Ed aka Homerraas).
The level warning light illuminates differently depending on if you have the low or the high cluster.
If you have the low cluster...the the little icon of the car with the arrows illuminates. If you have the high cluster...you'll get a text warning in the 20 digit alpha/numeric display if there's an issue with your leveling system (even though the icon can be seen in the cluster):