A straw in the wind
Definition 1 of 1
Pro Tip 1/3Subtle Clues
Use 'a straw in the wind' to describe barely noticeable hints about future events or decisions. 
His reluctance to discuss plans was a straw in the wind for the project's cancellation.
Pro Tip 2/3Figurative Speech
'A straw in the wind' is figurative for small signs, not literal straws or wind. 
The manager's hesitation was a straw in the wind, hinting at the merger.
Pro Tip 3/3Prediction Tool
It suggests you are using a sign to predict something before it's confirmed. 
The sudden quietness in the office was a straw in the wind that layoffs were coming.