All that is saying is that He will come from the east just as the sun rises in the east and sets in the west. The fact Christ says He will come like a thief and tells His followers to ‘watch’ implies’ His return could be missed if His followers are not ‘watching’. This puts to bed any automatic recognition as the command and prerequisite is to ‘watch’. Of what use is watching if everyone will automatically see Him?
I have understood the meaning is to be prepared for that day, because it will come when people don't expect it. But, when it comes, it will be as clear as lighting through sky, you will notice it without any effort.