Possible Clues:

• Boston street where Cheers is located
• Have life as a prisoner, giving a warning signal
• In the tube a constant light
• It's illuminating to do time?
• Warning light on hill or cliff
• Warning light on tower or hill
• Guiding device - signal fire
• Indulge in criminality? This may serve as a warning
• Shining light
• A trick? Be first to give a signal