Possible Clues:

• Sound familiar
• Vacuous, niggling Liberal parties seem familiar
• What door-to-door salesman's wont to do to jog one's memory
• Phone -- who invented it? Sound familiar?
• Signal to start class may awaken memories
• Circle a clanger and start to arouse memory
• Recall one of the first people carried by Circle Line
• Advice to cyclist to remind one of something
• Make an appealing sound, by the sound of it
• Toll is to jog memories