Responsibility
Responsibility is one of the story's most prominent themes. As the specter haunts him, the signalman finds himself in the dilemma of knowing that a disaster is coming, yet being unable to send out a danger message without being questioned by operators at either end of the line. The narrator takes pity on the signalman, observing how genuinely disturbed he is to be in a position where he is responsible for people's lives but has no way to take action. Worried about the signalman's mental health, the narrator feels the weight of his own responsibility, too, unsure whether it is his duty to report the man to the railway superiors or to have faith in the signalman, with whom he has developed a connection. The theme of responsibility is driven home with the story's final line, when the narrator notes that the train driver said "For God's sake, clear the way!"—a statement the narrator attached to the action the signalman earlier demonstrated for him. The line had only been heard in the narrator's head, suggesting that perhaps he played some part in the supernatural circumstances that led to the signalman's death.
Helplessness
As a counterpart to responsibility, the theme of helplessness affects both the signalman and the narrator. Though the specter warns the signalman of impending doom, the signalman is helpless to take action on the cryptic messages, as his usual decoding tools for telegraph messages are of no use. The signalman's sense of responsibility causes distress and he sits and waits helplessly for disaster to strike. The narrator, similarly, is unable to tell how much of the signalman's take on reality he should believe. His instinct is to discredit the specter's appearances as coincidences, but he can't shake the sense of eeriness he feels when he looks at the red light or hears the wind whistle through the tunnel. Even the specter is helpless to avert the disasters he preemptively mourns. Ultimately, both men are helpless to avert the coming disaster: the signalman can't move when the train cuts him down, and the narrator is too late to help.
Decoding Messages
The signalman's primary task is to decode messages. Morse code telegraph messages arrive in his signal box, which he writes down to decipher before taking action by changing signals and lights. Ironically, the specter arrives to deliver his own cryptic messages of disaster, which the signalman is ill-equipped to decode. Similarly, the narrator struggles to understand what the signalman is communicating, as he is unsure whether to believe the man's encounters with the supernatural or to doubt his grip on reality. Ultimately, the instances the narrator dismisses as coincidence prove to have accurately predicted the future.
The Supernatural
The primary question posed in "The Signalman" is whether the events of the narrative can be explained by coincidence and hallucination or if they are due to a supernatural source beyond scientific understanding or the laws of nature. The signalman himself does not doubt that he is truly seeing and hearing the specter, while the narrator prefers to believe the wind and his eyes are playing tricks on the signalman. The narrator also assumes the deaths that follow the specter's appearance are mere coincidence. However, the story ends with enough coincidences having stacked up that the reader is hard-pressed to believe they resulted from chance, suggesting that a supernatural source determined the train accidents and the signalman's death.
