Extinguisher, marks the spot of fire extinguishing system trigger so that marshals can easily locate it.
Neutral, marks the spot of switch that puts gearbox in neutral so that marshals could easily locate it.
E & N are doubled (exist in cockpit and outside of it too) while Ignition switch exists only inside of cockpit. Since N switch inside of cockpit is on steering wheel marshals can't use it because driver has to take it off in order to get out of the car and apart from that switches on steering wheels are very small and with no or very tiny marks.
http://www.marshalspost.com/display_art ... icle_id=24
