The very first sentence in Charles Dickens' short story The Signal-Man is, “Halloa! Below there!”

With this opening, Dickens' narrator proceeds to relate the story of his encounter with a railroad signal-man, whose initial reaction to the narrator's greeting from above is to look down the railroad track rather than up to where the greeting originated. His greeting being ignored, the narrator again shouts to the figure below, "Halloa! Below!" This time, the figure looks up to where the narrator is standing, at which point the latter shouts again, “Is there any path by which I can come down and speak to you?”

The signal-man's reticence, it is soon revealed, is a result of his encounters with apparitions and strange voices, the sightings of which are invariably followed by tragedy. The Signal-Man is a horror or ghost story. Dickens' setting is bleak, befitting the tone he hopes to set for the narrative that follows. Witness, for instance, the following description of the surroundings in which the solitary railroad worker exists:

"His post was in as solitary and dismal a place as ever I saw. On either side, a dripping-wet wall of jagged stone, excluding all view but a strip of sky; the perspective one way only a crooked prolongation of this great dungeon; the shorter perspective in the other direction terminating in a gloomy red light, and the gloomier entrance to a black tunnel, in whose massive architecture there was a barbarous, depressing, and forbidding air."

Dickens' narrator's description of the scene is definitely consistent with the genre into which The Signal-Man fits, something akin to the world of Edgar Allan Poe. The setting is dark and foreboding, and the signal-man's tale is one of unrelenting tragedy. That the narrator's greeting ("Hallao! Below there!") should coincidentally be that which warned of impending doom explains the signal-man's strange reaction upon hearing those same words from up above.

When the narrator arrives in the vicinity of the signal box, he greets the signalman with the following words:

"Halloa! Below there!"

On hearing these words, the signalman does not look up towards the narrator, as expected, but looks down the line. This causes the narrator to repeat the words and, this time, he is acknowledged by the signalman.

While these words may appear ordinary, they are, in fact, significant to the signalman. Later in the story, for instance, he reveals that he heard those exact words on "one moonlight night." The figure, to whom the voice belonged, appeared to be warning him about an impending accident, but it suddenly disappeared.

Six hours later, however, there was indeed an accident on the line in which numerous people were killed or wounded. For the signalman, then, these words are synonymous with that strange warning, and this causes him to be extremely wary of the narrator.