Where does authority extend when a station name designates the first named point in track warrant limits?

The correct choice indicates that the authority extends from and including the last siding switch when a station name designates the first named point in track warrant limits. This is significant in railroad operations as it clearly defines the boundaries of a train's authority to operate on the tracks.

By starting the authority from the last siding switch, it allows for the inclusion of any potential off-track or siding movements that may be necessary for the train. This provides an operational clarity that ensures the train can safely maneuver around other trains or facilitate loading and unloading activities at the station, enhancing efficiency and safety in train operations.

In instances where the other options are considered, such as starting authority from various points like a station sign or the first signal encountered, those do not take into account the need for flexibility and operational safety that comes from including the last siding switch as a landmark for authority.