On a Spitfire Hornet the kill button is mounted to a triangular plate which in turn is mounted on two of the top yoke handlebar bolts.

Hornets ('66/'67) is a button mounted in a chrome holder direct to the handle bar.

I can't tell what that last image is of.

1967 BSA Wasp
1967 BSA Hornet (West Coast Model)
1967 BSA Hornet (East Coast Model)
1968 BSA Firebird Scrambler
1968 BSA Spitfire Mark IV
1965 Cyclone Competition where are you?