About Timeline Marking
As you animate, the Timeline view will accumulate many layers and keyframes. You might want to identify them using coloured layers and scene markers.
Scene markers are visual indicators displayed at the top of the Timeline view in the frame counter area. You can use it to denote anything relevant to your work. You can indicate the frames you want to clean up, a change in action, an impact, or where you intend to apply an effect. You can also add a note to a scene marker, which is displayed when you hover over the scene marker.
There are two ways to add a scene marker. You can mark the current frame or make a frame range selection and mark the whole section.