How does blood signify Macbeth's guilt?

Immediately after Macbeth assassinates King Duncan, he looks down at his bloodstained hands and says,

"Will all great Neptune’s ocean wash this blood Clean from my hand? No, this my hand will rather The multitudinous seas incarnadine, Making the green one red" (Shakespeare, 2.2.61-64).

In the play, blood represents Duncan's murder, the consequences attached to Macbeth's serious crimes, and the feelings of guilt that both Macbeth and his wife experience following the assassination. The fact that Macbeth believes that all of the oceans in the world will not be able to clean the blood from his hands signifies his extreme guilt. Lady Macbeth responds to her husband's comments by saying that "a little water clears us of this deed." Ironically, Lady Macbeth also becomes overwhelmed with guilt and begins hallucinating, believing that her hands are constantly covered in blood.
In an attempt to secure his throne and establish a lasting legacy, Macbeth hires assassins to murder Banquo and Fleance. Following Banquo's death, Macbeth begins to hallucinate and sees Banquo's ghost during a banquet. After Lady Macbeth persuades the Scottish lords to leave, Macbeth says,

"It will have blood, they say. Blood will have blood. Stones have been known to move, and trees to speak" (Shakespeare, 3.4.128-130).

Once again, Macbeth's comments about blood correspond to the guilt he feels regarding his crimes. His thoughts of blood indicate that he has not forgotten about his horrific crimes, which continue to haunt him.