‘straw in the wind’?

What would happen if you were to leave a straw in the wind? It’ll probably get blown away; but in the process, it will tell you something. It will give you information about the direction in which the wind is blowing. When you say that something is a straw in the wind, what you mean is that it is a sign of things to come; a small hint of what is likely to happen in the future.

*There are straws in the wind which suggest that the two companies will go belly up.

*The constant bickering is a straw in the wind indicating future problems for the newly married couple.