Ok, so just as a change to FiestaST's posting of photos of the infamous button, I decided to do a live test of something somebody described here: pressing the car's ignition button instead of the disable S/Sbutton (well done BMW on deciding to put those two right next to each other behind the damn steering wheel where you can't even see them).
No animals were harmed during this test (myself included): I did it at 10km/h in my parking lot at home.
The result: prodding the car's ignition button quickly while the car is in motion does nothing (at least in my BMW F30 320i). A quick press is all it takes to disable the S/S, but the car just ignored the same on the ignition button while it was in motion. Not to be deterred I then tried pressing in the ignition and holding it in ... and sure enough at around two or three seconds the engine turned off.
At this point my car was very unhappy with me and warned me that the car was still in motion in D mode although the engine was off. As soon as I hit the brake, the car automatically shifted into P mode (which jerked the car to a stop). Restarting was easy: I just had to hold down the brake, shift back into drive and continue like usual.
And there you have it. If this was a fear keeping you up at night, fear not (but probably just test it first in a parking lot)