A bit late to the party, but my understanding (from our safety camera people) is that the markings are required from an enforcement perspective as a secondary means to determine speed – legally you require two methods of speed detection for the fine to be valid. The camera takes two photos, and speed can be determined by the measured distance between markings and the known interval between the two pictures.
The markings clearly only need to be on the side of the road where speed measurement and enforcement is taking place, and there is no requirement for them to be raised (unless the specific model of camera requires it to see them properly?).
There is no relation between these markings and TSRGD as Simon states – hence they can be used through yellow boxes etc without affecting their enforceability.