Here is a simple drawing of a kill switch for an external ignition module like a Brison or ZDZ.

I could not find any reference to a kill switch in the AMA Safety Code.

I did find this in the IMAA Safety Code if you are flying in an IMAA Sanctioned Event:

SECTION 5.0: EMERGENCY ENGINE SHUT OFF (Kill Switch)

5.1 Magneto spark ignition engines must have a coil-grounding switch on the aircraft to stop the engine. This will also prevent accidental starting of the engine. This switch shall be readily available to both pilot and spotter/helper. This switch is to be operated manually and without the use of the Radio System.

5.2 Engines with battery powered ignition systems must have a switch to turn off the power from the battery pack to disable the engine from firing. This will also prevent accidental starting of the engine. This switch shall be readily available to both pilot and spotter/helper. This switch shall be operated manually and without the use of the Radio System.

5.3 There must also be a means to stop the engine from the transmitter. The most common method is to close the carburetor throat completely using throttle trim, however other methods are acceptable. This requirement applies to all glow/gas ignition engines regardless of size.

Ken