Related Clues:

• 'What's ___?'
• One of 39-Across
• Fingerprint or dropped handkerchief, say
• This, for example
• Detective's need
• Print, maybe
• 'See ___?'
• It may be found with a magnifying glass
• Guiding light?
• Inkling
• Fingerprint, perhaps
• Sleuth's find
• Airhead's lack?
• Not that
• Footprint, maybe