What was Jesus’ response to the question at Matthew 24:3: “When will all this happen? What sign will signal your return and the end of the world?” (NLT).
What will be the sign? Does the context say anything about “the last days”?

First, “Jesus answered: ‘Watch out that no one deceives you.'” (Matthew 24:4)

Mark recorded: “Watch out that no one deceives you. Many will come in my name, claiming, ‘I am he,’ and will deceive many. ” (Mark 13:5,6)

And in Luke: “Watch out that you are not deceived. For many will come in my name, claiming, ‘I am he,’ and, ‘The time is near.’ Do not follow them. When you hear of wars and uprisings, do not be frightened. These things must happen first, but the end will not come right away.” (Luke 21:8,9)

When anyone is preaching that “The time is near,” Jesus said to avoid them, “Do not follow them.” 

Jesus said there will be wars, uprisings, disturbances, wickedness, lawlessness, hatred, persecution, loss of love, great earthquakes, famines, pestilences, fearful events, persecution, etc. (Matthew 24:6-12; Mark 13:7,8; Luke 21:9-12). Are these to be something new, or different, or on a greater scale, than the past? Not really. These events are “business as usual” for this world.

“Then you will be handed over to be persecuted and put to death, and you will be hated by all nations because of me.” (Matthew 24:9)

“For false messiahs and false prophets will appear and perform great signs and wonders to deceive, if possible, even the elect.” (Matthew 24:24)
False prophets will have counterfeit signs the , and make false predictions – reject them.

According to the Bible, “the last days” began with the first coming of Jesus back in the first century (Hebrews 1:2 NIV; Acts 2:17).  Paul’s warning in the 60’s of the 1st century about bad people “in the last days” (2 Timothy 3:1 NIV) was current, because he advised, “Stay away from people like that” (2 Timothy 3:5 NLT). All Christians, back then and now, are warned to try to avoid bad people.

The apostle Peter referred to “scoffers” “in the last days”, saying that “they deliberately forget” important facts (2 Peter 3:3-5 NIV). This also shows that “the last days” were then current.

So, the events of the last days that are predicted and explained in the Bible would stretch all the way from the time of Jesus until the end of this world at his second coming. Are these bad things an indication that the end is near? No, because Jesus said, “But about that day and hour no one knows, not even the angels in heaven, not the Son, but only the Father” (Matthew 24:36 NIV)! The end will come suddenly, without any warning, because Jesus also said to his disciples, “So you also be ready, because the Son of Man will come an hour that you do not expect him” (Matthew 24:44 NIV). We must be ready at all times, because no one will ever be able able to figure out when Jesus will return.

What about the “sign” Jesus was asked about in Matthew 24:3?  The context says nothing about “the last days”, as is often claimed. There will be no advance “sign” of Jesus’ return until the very end, when he has returned with destructive power. The “sign” will suddenly occur at the moment of his return (Matthew 24:29):

“Then will appear the sign of the Son of Man in heaven. And then all the peoples of the earth will mourn when they see the Son of Man coming on the clouds of heaven, with power and great glory”—Mathew 24:30 NIV

Jesus said, “the world will not see me anymore” (John 14:19 NIV). He will not be visible at his return. In the Bible, “clouds” can denote invisibility. This becomes obvious when we consider Revelation 1:7: “‘Look, he is coming with the clouds’ and ‘every eye will see him, even those who pierced him’; and all peoples on earth ‘will mourn because of him'” (NIV). Since “those who pierced him” are long dead, the language here is figurative. Yes, Jesus is definitely “coming”, but he will not be literally visible. That is why a “sign” is needed that indicates his return has occurred. This “sign”, or “signal” (Matthew 24:3 NIV), will be so obvious that everyone on earth will know that Jesus has returned, albeit invisibly.