There are several images that are symbolic in Macbeth.  Some to remember are the floating dagger, Lady Macbeth’s spots, and Macbeth’s head.

First of all, the floating dagger is an important image.  The dagger is imaginary.  Macbeth imagines it when he is trying to decide whether or not he should kill Duncan.

Is this a dagger which I see before me,

The handle toward my hand? Come, let me clutch thee.

I have thee not, and yet I see thee still. (Act 2, Scene 1, p. 27)

This image is important because we know that Macbeth is thinking about murder, and he seems to view the dagger as leading him to kill Duncan.  We see it as a sign of his madness.

Another important symbolic image is Lady Macbeth’s blood-spotted hands. 

Out, damned spot! Out, I say! One–two—

why then ’tis time to do't. Hell is murky. Fie, my lord, fie!

A soldier, and afeard? (Act 5, Scene 1, p. 77)

At the end of the play, Lady Macbeth’s attitude has completely changed.  She is no longer excited about murder.  She is guilt-ridden, and her guilt has led to madness.  Blood is a constant presence in the play, and this vision of blood is significant for being imaginary and a manifestation of guilt.

The third important image is Macbeth’s head.  It is significant that Macduff beheads him and holds his head up.

Hail, King! for so thou art. Behold where stands

The usurper's cursed head. The time is free. (Act 5, Scene 7, p. 90)

Just as you cut off the head of a snake to end the danger, Macbeth is the head of the country and his beheading symbolizes the end of his tyrannical reign, the end of his suffering, and the end of the play.