What does John 2:24 mean?

Jesus was careful not to "entrust" Himself to the people in Jerusalem. Jesus had a supernatural wisdom for knowing people's hearts and minds. He knew that many of them were only interested in entertainment. Jesus' conversations with the Pharisees, and His miracles, certainly provided a good show. Over time, people would fall away as they realized that fireworks were not the main purpose of Christ's ministry. God doesn't jump through hoops, simply to keep us amused.

Also, those who say "only a miracle will make me believe," probably won't believe even if they see one (Luke 16:30–31). Simple intellectual belief is not the same as saving faith. The gospel requires each person to trust in Christ, not merely admit that He exists, or that He has power. It's likely that these unspecified signs from verse 23 are what inspired Nicodemus to seek Jesus out, as described in John chapter 3. He knew that true miracles were messages from God, and that only someone bringing God's message could do the things Christ did.