It's meant to be an ice warning - that's the temp it starts to form on the road.
Note that you shouldn't rev too high (I use 4k) while the engine is cold, as the oil doesn't flow as well.
Can't imagine a system that keeps revs higher than 2k while the engine is cold.

 

The Echo's system didnt make sense to me either. but it really did run the car harder until he heated up. the light would eventually kick off, and the car would shift as normal. but oh well. very thoughtful of mini to include that warning device i guess.

 

Only that it's cold and you should watch for ice. You get the chime if the temp drops to 37F, regardless of whether your car engine has been running for hours and it's warm or not.

One of the carry-overs from BMW, which has had this in the 3-series since at least 2000.