You can make explicit why they want to see a sign. AT: "to see a sign from you that proves what you say is true" (See: [[rc://en/ta/man/translate/figs-explicit]])
# An evil and adulterous generation seeks for a sign ... given to it
Jesus is speaking to his present generation. AT: "You are an evil and adulterous generation who demands signs from me ... given to you" (See: [[rc://en/ta/man/translate/figs-123person]])
# adulterous generation
Here "adulterous" is a metaphor for people who are not faithful to God. AT: "unfaithful generation" or "godless generation" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Jesus would not give them a sign because, though he had already performed many miracles, they refused to believe him. This can be stated in active form. AT: "I will not give it a sign" or "God will not give you a sign" (See: [[rc://en/ta/man/translate/figs-activepassive]])