The word 'vane' comes from the Anglo-Saxon word 'fane' meaning 'flag'. And you can see many weather vanes featuring the "flag". The Bayeux Tapestry of 1070s depicts a scene, with a man installing a weather vane with a cock on Westminster Abbey, while the dead King Edward is carried inside.
The weather vane is a lovely architectural ornament to show you the direction of the wind, although not so functional one thing we can tell, it is very decorative. Often featuring the traditional cockerel design with letters indicating the points of the compass, you can find it at the highest point of a building.
In the 9th century the Pope issued an edict that all churches must show the symbol of a cock on its dome or steeple, as a symbol of Jesus' prophecy of Peter's betrayal , that Peter would deny him three times before the rooster crowed on the morning following the Last Supper. Many churches started using this symbol on its weathervanes.
Top row: Chamberlayne Road, Chevening Road, Walm Lane.
Middle row: Old Gloucester Road, Willesden Green Library, Gladstone Park
Bottom row: Hanover Square, Tower of London, Temple Place.