Luke 21:7

And they asked him, saying, Teacher, when therefore shall these things be? and what shall be the sign when these things are about to come to pass?

Jesus went far beyond answering the question recorded here. He did indeed give the sign that signaled the end of Jerusalem and the temple (Luke 21:20); but as Geldenhuys noted:

So terrible, the Saviour warns them, will be the judgments soon to burst forth over the people of Jerusalem, that the judgments upon the guilty city will be the foreshadowing of the Final Judgment at his Second Advent.[13]

In the meanwhile, for Jesus clearly foresaw that the destruction of Jerusalem was not to occur for a whole generation, the Lord carefully warned the Twelve not to be deceived by many developments that would only appear to be signs; but as reiterated in Matthew, "The end is not yet." Luke 21:8-19 inculcate the warnings against false signs.