Currently you cannot select a Marker in the marker track and S1 starts playback from there. It selects the Marker for editing.
You should be able to just select the marker with the mouse and it plays back from there. There is no need for first selecting it then having to do a keyboard key L to do this.
It would be a great feature if:
1. Left mouse click starts playback from selected marker in the marker track
2. Double click on marker actually selects the marker and opens it for editing