A well-known miracle makes us think a bit harder about "signs". 

The healing at the Pool of Bethesda is a great story, but the more we look at it the more questions arise. One obvious one is why just this man was healed when there were 5 covered porches of "sick crowds" by the pool. It is also fascinating that John records this miracle as a sign that can help believers maintain confidence in Christ, and yet the religious leaders who witnessed it were far from persuaded.