What does Matthew 16:3 mean?

And in the morning, if the sky is red and gloomy, you say, "Today will be stormy." You know how to read the sky, but you can't recognize what's happening right in front of you. This generation is evil and unfaithful. You're asking for a sign, but the only sign you'll get is what happened with Jonah.' Then he left them and walked away. Matthew 16:3 - Modern Text Bible

(He criticizes them for missing the spiritual signs all around them, and says the only sign they'll get is the story of Jonah—a hint at his own resurrection.)