The correct answer is B. T/809.
In case of block forward, private number of the station from which the shunting movement is to be started is written on shunting authority. This is done to ensure that the shunting movement is authorized by the proper authority and that the receiving station is aware of the movement.
Option A, T/806, is the private number of the station to which the shunting movement is to be made. This number is not written on the shunting authority.
Option C, T/809, is the private number of the station from which the shunting movement is to be started. This is the correct answer.
Option D, T/810, is the private number of the station that is to act as the intermediate block post. This number is not written on the shunting authority.