It's the 'Warning: Trophy' light. Some kind of prize awaits you after you go another 700 miles. But seriously, it's the Service Requirements symbol however the manual is quite vague about it's purpose. I think it has to do with FOB info and only BMW can unlock the secrets behind that door.
Sometimes I'm up, sometimes I'm down
Other times I'm probably found
Somewhere between a pair of huge
Speakers pushed by vacuum tubes