Related Clues:

• Sign of things to come
• Forewarning
• Symbol
• Sign of foreboding
• Dark clouds on the horizon, say
• Portentous event
• Dark clouds, say
• Evil sign
• Hooting owl, maybe
• *Eclipse ... black cat ... future
• Pickup line request
• Warning
• Writing on the wall
• Speak with one's hands
• Ampersand, for one