Hi Colin - Binding assets to a session layer is good for hiding unwanted scenery such as trees but not good for rolling stock, in my opinion, anyway. The rolling stock will still be on the track and if you make it invisible then you will find it difficult to place a new piece of stock on top of the invisible one. As your train drives it will suddenly couple with invisible stock and cause a disaster.
Trackmarks existing on a route can be made invisible by the above means and in Surveyor those marks do not appear on menus but unfortunately (as far as I know), in Driver the trackmarks do appear in menus. It would be much more useful if invisible bound trackmarks and triggers etc were also invisible to the driver commands in Driver mode.