Big idea: The ultimate sign is the resurrection.
I once had a conversation with someone where I asked what evidence they would need to believe in God. They told me that if God personally sent them a message, then they would believe. Personally, I was skeptical and told him so. "If you heard a voice, you would assume it was a hallucination." He admitted I was right. I do not remember the specifics of how the conversation went after that (except that it was unfruitful), but I wonder if he might have suggested that other people also needed to see God at the same time he did, or perhaps hear the message. Where do we draw the line of sufficient evidence?
Jesus did not say that the evidence of who He was would be the turning of water into wine or the healing of a blind man. Instead, He told them, "Destroy this Temple and in three days I will raise it up again." They did not understand, or they would have killed Him on the spot. Any blasphemy they might have thought He was committing by saying He could build the Temple so quickly was nothing compared what He was really claiming: to be the place where Heaven and Earth met, the place that people could find peace with God, and the place of true worship. What evidence did He offer for such a claim? That when they destroyed that Temple, He would build it again in three days. They could kill Him, but they could never stop Him.
Discussion idea: Why is the resurrection a better sign than any other? Here is a debate about the evidence for the resurrection which may be interesting: https://www.reasonablefaith.org/media/debates/is-there-historical-evidence-for-the-resurrection-of-jesus-the-craig-ehrman/
Prayer focus: Lord, help me to trust you. Not simply blindly, but recognizing that You have already given the ultimate proof. If you conquered death, no problem I face can compare. If you gave your life, nothing could be beyond your love.