Many of the prophecies on Jesus were given as signs in the Old Testament. This is how God does things: He does not always tell you what is going to happen straight out, sometimes He uses figurative language (Just as how Jesus used parables) to make a point or prophecy. Sort of like the prophecies of the end times in Revelation with the seven heads (supposedly representing 7 nations), etc. But do not rebuke signs which you do not understand.