The Tri-ang Fog Signal is an interesting trackside feature which dates from the 1960s. It was sold both in the UK and in overseas markets and the lower picture, above, shows a 1965 Canadian Catalogue illustration - thanks to the Tri-ang Railways website.
The Fog Signal is a clip-fit accessory that is mechanically operated. With the lever in the cocked position, it is struck by a passing loco; this then releases the trigger situated within the lineside hut which, in turn, fires the maroon.
The maroon is, actually, a roll of caps which had to be bought separately.
The Catalogue Nº for the Fog Signal is RT 267 and it was available in the mid-1960s.