Related Clues:

• Formal greeting
• Wave down, as a taxi
• Like good watchmen
• Stones from the sky
• Fully awake
• Bright-eyed
• Cab signal
• Give a heads-up
• ''Ave!''
• Greet with acclaim
• Balls of ice
• Type of post-caffeine state
• Percipient
• Summon, as a cab
• ''Heads up!'' e.g.