What tells us summer has come?

[Silverobama]

I want to know how can I ask the question "What are the signs of the summer?" naturally in English.

How about "What tells us summer has come?". The possible context is in a class teaching kids English about seasons.

 

[SoothingDave]

I think your original is better. The calendar tells me that summer has come. The news media tell me.

"What are the signs that summer has come/is coming?" is natural.

 

[probus]

It varies from one locale to another. In dixieland, for example, rednecks out in their wife-beaters is a sure sign that summer has begun.