Jesus often appeared discouraged with those who wanted signs and were disinclined to put their faith in the power given to Him by His Father in heaven. He knew that, in actuality, no sign would give them faith; they would find themselves entertained by the "magic" of the sign and then move on to something else. They would totally miss the power and the authority behind such a sign.
Jesus points to the sign and the preaching of Jonah (a "mere" prophet) and how he led the Ninevites to repentance; yet, they had one among them who was far greater than Jonah. They couldn't see Him for who He was or understand what He was about. He was just too familiar for them.
Let us pray that the Holy Spirit will help us recognize when the power and presence of Jesus are active in the ordinary moments of our everyday lives; may that recognition lead us to greater faith in God's love, mercy, and active presence in our midst.