Final answer:
In the story, 'The Murders in the Rue Morgue,' Dan notices a card-rack hanging next to the file cabinets. This card-rack contains visiting cards and a letter, catching Dan's attention.
Step-by-step explanation:
In the story, 'The Murders in the Rue Morgue,' the main character, Dan, notices a trumpery filigree card-rack hanging next to the file cabinets. This card-rack is made of pasteboard and is attached to the mantelpiece by a dirty blue ribbon and a little brass knob. The presence of this card-rack is significant because it contains visiting cards and a letter addressed to the minister, which catches Dan's attention.