@helian43 - The normal use of a trackmark is for the train to drive until it enters the trackmark. There is a driver command <kuid:131986:1054> which monitors a specified junction and stops the train when it leaves that junction. The variation that I made monitors a trackmark instead of a junction.
The main issue is that the stopping point varies greatly, depending on the mass of the train, its speed, its length, and the braking effort of the loco. Measures need to be put in place to limit the speed of the train at the time when "the end is nigh".
Hope that answers your question - och aye?