Note to Macbeth, Act 5, Scene 8, lines 54-55:

"Behold, where stands / The usurper's cursed head"

Act 5, Scene 8, line 54.
According to Holinshed, Shakespeare's primary source for Macbeth, Macbeth's head was placed on a pike. In Shakespeare's time, traitors' heads were placed on pikes and mounted over the south entrance to London Bridge, very near Shakespeare's Globe Theatre.