Thanks for additional info

I have seen a lot of blue prints and work drawings [nothing from WW1] for this but I have never seen details like this, even no signal pistole. Engineer was focused on the main technical view of the construction. But place where details like this could be seen is the service manuals and there should be written instruction as well sketch for this.
Again I am not of help but hope that my experience in other field could be of idea where to search.