Hi All,
Not wanting to be flippant

but the picture that Judy posted is a First World War one. There was no such Corps as the Royal Signals at this period. This task was carried out by a the Signals Branch of the Royal Engineers. During the First World War, mounted troops (of any Corps or Regiment) would be issued with a clasp knife and lanyard. If the knife was dropped whilst on horseback, it was a pain in the backside to retrieve, and also increased the chances of it being lost. This problem was remedied by having the knife tied to the person, and placed in the top left pocket.
Mounted troops generally had an ornate, blanco’d one for walking out etc.
Lanyards became a decorative item of dress - for some Corps and the Infantry – after the First World War, especially with the advent of Battledress, when it became common for infantry regiments to wear one (Parachute Regiment: Maroon, Blue, Green, etc.). As they were purely decorative, you won’t find very much at the end of it.
Have a look at the picture attached it shows various ranks of the Royal Engineers, during the First World War. Note the absence of a Royal Engineer's black lanyard – as at this time, it did not exist. However, those Royal Engineers on mounted duties have a lanyard.
The Horseshoe badge that some are wearing is Farrier and Shoeing Smith.
Hope this helps
Tom McC