In Charles Dickens' short story "The Signalman," the author conveys clear characteristics in the subject of the title in order to further develop the eventual sense of horror that descends upon the narrator, and perhaps the reader as well.
Dickens describes the signalman as someone who is never of what he has seen and haunted by it, but also as a masterful signalman who does his job well and with care and great accuracy. In this way, Dickens shows the reader that this is a man to be trusted. He is a reliable voice in the story, so the reader (and the narrator) are inclined to believe him and take him seriously.
The signalman is also a caring individual. He expresses to the narrator that he cannot understand why a specter would visit him and not provide him with the details or means to prevent the death of the individual the ghost is warning him about. It is distressing to him to know something must be done, but he knows not what or how to do so.
In allowing us to see the kind of man he is, and in sharing with the reader the careful professional he is, we expect that he will be always vigilant, looking for a way to avert disaster. However, perhaps because he is all of these things, his death is that much more horrible as the specter must be the thing that leads him onto the track, to a place he would usually no better than to venture.
Losing sight of what he knows of his job, he allows himself to become unmindful of his surroundings in looking for answers, and he becomes the latest victim, as foreshadowed by the ghost's warning.