For what specific reasons can Jews ask for a sign?

This question was prompted by these verses surrounding Jesus' cleansing of the temple of the money-changers: **John 2:18-19** (NKJV): > So the Jews answered and said to Him, “What sign do You show to us, > since You do these things?” > > Jesus answered and said to them, “Destroy this temple, and in three > days I will raise it up.” On what basis could Jews demand a sign from someone?