When Fortunato doesn't believe that Montresor is a mason, Montresor pulls out a trowel and shows it to Fortunato. The event of Montresor showing the trowel to Fortunato foreshadows the event of Montresor using the trowel to bury Fortunato alive.
The motto of Montresor's family is also an example of foreshadowing because it says that no one will insult him without punishment. When he tells Fortunato this, it foreshadows that since Fortunato insulted Montresor, he will be punished.
Fortunato's love of wine and his costume is also an example of foreshadowing because he loved wine so much that he would do anything for wine. He was also dressed as a jester which foreshadowed his foolishness. It foreshadowed that he would believe Montresor and that he would be foolish and naive.