I don't blame the Pharisees in today's Gospel one bit. "Teacher, we would like to see you work a sign." Herod hoped for the same thing when Jesus was brought to his court. In our day, we might not be so blatant about it, but I suspect there's something in all of us that would like to put God to the test--a test of our own devising. One that leaves us in charge.
But the saints asked for signs, too.
St. Ignatius of Loyola proposed asking God for an external sign or manifestation of his will as a confirmation of the grace of discernment, but he seems to have left the exact form of that sign up to God. Ignatius trusted that when a sign was given, we would also be given the grace to recognize it.
Isn't that how it worked in the Bible, generally? Moses noticing the burning bush; the Ninevites listening to Jonah; the Queen of the South responding to reports about a surpassingly wise king; Elijah in the cave recognizing the whispering breeze... God's signs came unbidden.
How many signs might God put across my path every day without my noticing, wondering, paying attention--and so I come to Jesus and say, naively, "I would like to see you work a sign."