Whenever readers approach a literary narrative, they must always place the work in its historical context. With O. Henry's short story, the setting is most likely New York at the turn of the twentieth century. At that time policemen walked a beat, meaning that there was a policeman who had a certain section of the city to patrol by walking around in it. During this time, he checked that doors to stores were locked and that there was no suspicious activity. When Jimmy, the policeman of O. Henry's story, notices a stranger in the doorway of a darkened hardware store, he is a little wary. However, when he approaches, the man explains what he is doing very quickly.
Of course, the surprise ending of the story evolves because this man lights up his face as he ignites his cigar. Jimmy Wells, the policeman, moves on down the avenue he patrols, but he contacts the police station which searches through their information on suspicious persons. So, in his letter to his old boyhood friend, explaining why he has not been at the appointed meeting place, Jimmy alludes to a telegram--"wires us"-- that the police from Chicago had sent to the police in New York regarding "Silky Bob." For, in the early 1900s, the telegraph was the quickest and most reliable method of communication. The telegram sent messages by means of wires strung all over the US. People used the Morse Code to send these messages.
Although it was possible to send messages by wire, it was not possible to send pictures. The Chicago police could not have sent the NYPD either a sketch of 'Silky' Bob or a photograph. They would have had to give a verbal description. This would naturally have included any identifying marks or items of apparel. O. Henry's description of the man in the doorway includes two distinctive identification marks.
The man in the doorway struck a match and lit his cigar. The light showed a pale, square-jawed face with keen eyes, and a little white scar near his right eyebrow. His scarf pin was a large diamond, oddly set.
The man has a little white scar near his right eyebrow, and his scarf pin is a large diamond, oddly set. The white scar is a good way of identifying Bob, but it is not infallible. A lot of men could have scars near their eyebrows. The large diamond is not infallible evidence either. No doubt it was common for men in those days to wear jeweled tie pins and scarf pins. But the words "oddly set" are a dead giveaway. The telegram from the Chicago Police would, of course, have contained a precise description of the scarf pin's setting. It would have been one-of-a-kind. We can picture it as a large diamond surrounded by smaller contrasting jewels like rubies or emeralds. O. Henry's description of Bob when he lights his cigar is not intended to help Jimmy recognize his old friend but to give Jimmy two strong clues that Bob is the man wanted in Chicago. Jimmy has no reason to doubt that the man standing there in the doorway is his old friend Bob, but Jimmy would have no way of knowing that Bob was the man wanted by the Chicago police except for the white scar and the "oddly set" scarf pin. O. Henry never mentions Bob's last name. It would appear that the Chicago police know the wanted man only by his nickname of 'Silky' Bob.
Why did Bob strike a match and light his cigar at that point? Probably for at least two reasons. One was to show the policeman that he felt perfectly at ease and was not afraid to show his face. The other reason was probably that lighting his cigar was a way of demonstrating that he was standing inside the doorway because he could hardly light his cigar outside in the rain. Bob probably also wanted the policeman to see his flashy clothes and his diamond scarf pin. Such an affluent man would hardly be planning to burglarize a hardware store.
No doubt Bob did not want the policeman to ask to see some identification. This is perhaps the main reason that Bob takes so much trouble to explain why he happens to be standing there late at night.