There are several symbols of which Lady Macbeth speaks in the play Macbeth. In Act 2, Lady Macbeth says that she hears an owl shriek when her husband is supposed to be murdering King Duncan. She calls the owl the "fatal bellman" which symbolizes the death of King Duncan.
However, the more well-known lines delivered by Lady Macbeth occur in Act 5 of the play. Here, Lady Macbeth shows her guilt over helping her husband commit murder early in the play. She has learned that Lady Macduff and her entire court have been killed, and Lady Macbeth cannot forgive herself for her role in her husband's crime. Here, Lady Macbeth says, "Out, out damned spot!" and makes like she is washing her hands. This symbolizes the "blood" that she sees on her hands and represents her overwhelming sense of guilt.