So around 2:20 in this video here https://www.youtube.com/watch?v=YyfcrqK5DjU it shows him going into the N menu and playing around with the Emergency Signals. When he starts explaining the E and J thing the J key is doing absolutely nothing. I've tried changing the Emergency Signals from lights to lights & sirens and still J is doing nothing. If it's on Lights then E will turn just the lights on if it's on Lights and Sirens then E will turn that on. At the bottom of the User Doc it says it's a function too "In addition to the menu itself, the J key also forms part of the interaction system, allowing for the toggling of an emergency vehicle’s siren."