How does a coast station notify a ship that it has a message for the ship?

A coast station notifies a ship that it has a message by transmitting, at intervals, lists of call signs in alphabetical order for which they have traffic. This method allows ships listening to the coast station to identify when there is a message specifically directed to them based on their registered call sign. The call signs are a unique identifier for vessels and are easily recognized by the crews on board.

By utilizing this systematic approach, the coast station ensures that ships within its communication range are kept informed about any pending messages without requiring constant direct communication, which could be inefficient. This practice helps maintain organized and effective communication, especially in busy maritime areas where many vessels may be present.

The other methods listed, while valid communication techniques, do not serve the same purpose as notifying ships of specific messages awaiting them. For instance, making a directed transmission on specific frequencies would typically be used for more immediate communication rather than for general notifications of message availability.