Summary: An adulterous generation has no reason to expect signs.
27 And it came to pass, as he spake these things, a certain woman of the company lifted up her voice, and said unto him, Blessed is the womb that bare thee, and the paps which thou hast sucked.
28 But he said, Yea rather, blessed are they that hear the word of God, and keep it.
29 And when the people were gathered thick together, he began to say, This is an evil generation: they seek a sign; and there shall no sign be given it, but the sign of Jonas the prophet.
30 For as Jonas was a sign unto the Ninevites, so shall also the Son of man be to this generation. KJV
Many of us have some folks in our family tree that we are proud of or proud of our heritage in some way. We may have sons and daughters who have risen above our status and we are proud of their success. We may envy someone else just as this lady would have been proud to be the mother of Jesus and thus praised her. Yet, Jesus says that if you really want to be blessed you have to hear the Word and keep it. Often our infusion of the Word is by sight, but also by the ear and then we must hear as in heeding it as well.
If this is not an evil generation, I don't want to see one that is and yet we are a generation of sign seekers. If we were taking in more of the Word it would be easier to debunk false prophets and to have sound doctrine instead of being tossed to and from by every wind of doctrine and sleight of hand by cunning men. We would avoid foolish fads to attract people and instead concentrate on sound doctrine and holy living. If you are going to put out wildfire you have to have plenty of the Word's holy water to immerse it.