Related Clues:

• Approval, so to speak
• Muffled ''Hey, you!''
• Discreet call
• Verbal elbow
• Surreptitious attention-getter
• Show boredom
• Subtle auction bid indicator
• Call to attention?
• Make a slip
• Subdued attention-getter
• ... a cheater in class
• Eye signal
• Discreet attention-getter
• See 24 Across
• Sound that may turn heads