Interesting video describing the procedure for departing trains at this station. First, the departure warning bell(for down trains) or the single tone "buzzer" (for up trains) is sounded. Once all passengers have boarded, the platform supervisor activates the ト indicator visible above the platform. The guard then closes the doors, and once the red indicator lights on the train car bodies extinguish, the platform supervisor activates the O indicator located in the same housing as the ト indication. The guard then signals all clear with the cab buzzer, and the train departs. The first train shown is a terminating service, so the above procedure is better represented by the second train and subsequent trains.
*I didn't know the departure warnings were different for up and down trains. This procedure is also followed at Yokohama Station, which also has platform supervisors working from elevated podiums.