Perhaps you've heard of the expression,"For whom the bell tolls, it tolls for thee." This bell at London's St. Sepulchre-without-Newgate is the physical embodiment of that saying.
At midnight on the eve of a condemned man's execution, and the bellman of St. Sepulchre's Church rang this bell 12 times outside the person's cell. As the prisoner was led out of Newgate Gaol and across the street while being taken to Tyburn Tree to be hanged,the following lines were read out:“All you that in the condemned hole conclude lie,
Prepare you, and for tomorrow you shall die.
Watch all,and pray, the hour is drawing near, and
That you before Almighty God will appear.
Examine well yourselves,in time repent,
That you not to eternal flames be sent, or
And when St Sepulchre’s bell tomorrow tolls,
The Lord above hold mercy on your souls.”The convict was then given a set of rosary beads in the hopes that they would repent their sins as they were led to the gallows. This custom began in the 17th century and continued for the next 200 years. There are references to the Bell in John Webster's The Duchess of Malfi and William Shakespeare's Macbeth.
Source: atlasobscura.com