Almost certainly some form of bulb horn.
And possibly sourced as an accessory.
Factory fitted didn't come until VERY much later ?
(Is anything shown at all in the brochure)

This has been discussed here before - for a later era.
Older types are skinny, later ones plumper and/or curlier (?)
P&H was mentioned, to match the headlamp etc type.
But this is possibly wishful thinking ?