How does lady macbeth signal when macbeth is to murder duncan?

As Macbeth shrives to success guilt overcome’s Macbeth where he can no longer think straight. Initially Macbeth planned was to kill Duncan but it wasn’t enough he also had to kill Banquo and Macduff’s family. Lady Macbeth realizes that nothing could ever get rid of the smell of the blood and the guilt caused by all the murders committed by Macbeth. "Here’s is the smell of blood still. All the perfumes of Arabia will not sweeten this little hand.