It is not hidden, covered, obfuscated, or even in a weird location. It’s literally sitting right on the door handle. Also even with a standard 1990 car with fully manual doors you are not going to be escaping out the doors if your car falls into water. The pressure differential of the water pushing against your door prevents you from opening it until the entire inside of the car has filled with water, MythBusters did a whole episode on this back in the day if you want to go find that for the full story. But the tldr is that once your car is in the water you’re only Escape options are to break the window, get the window rolled down, or wait until the entire car has filled with water and the pressure equalizes

Edit: turns out this is only in the M3, the Y, X, And CT are all designed by absolute idiots, and i joined them by not looking into all models