The Sign of the Son of Man
Matthew 24:30   and then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. 31And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
This is the Pre-tribulation rapture of the Israel of God, Ephraim and his fellows. Jews: Judah, Levi and Benjamin go through the tribulation and we are joined at the end of the seven years, as one in His hand.
Luke 21:27 And then shall they see the Son of man coming in a cloud with power and great glory. 28And when these things begin to come to pass, then look up, and lift up your heads; for your redemption draweth nigh.
Where is the sign of the Son of Man? In the clouds of heaven!
Mark 14:61-62 But he held his peace, and answered nothing. Again the high priest asked him, and said unto him, Art thou the Christ, the Son of the Blessed? 62And Jesus said, I am: and ye shall see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.
This is the description from Ezekiel 1:4And I looked, and, behold, a whirlwind came out of the north, a great cloud, and a fire infolding itself, and a brightness was about it, and out of the midst thereof as the colour of amber, out of the midst of the fire. 
And again: Ezekiel 1: 26-28 And above the firmament that was over their heads was the likeness of a throne, as the appearance of a sapphire stone: and upon the likeness of the throne was the likeness as the appearance of a man above upon it. 27And I saw as the colour of amber, as the appearance of fire round about within it, from the appearance of his loins even upward, and from the appearance of his loins even downward, I saw as it were the appearance of fire, and it had brightness round about. 28As the appearance of the bow that is in the cloud in the day of rain, so was the appearance of the brightness round about. This was the appearance of the likeness of the glory of the Yahuweh. And when I saw it, I fell upon my face, and I heard a voice of one that spake.
Psalm 68:32-35   32Sing unto God, ye kingdoms of the earth; O sing praises unto the Lord; Selah: 33To him that rideth upon the heavens of heavens, which were of old; lo, he doth send out his voice, and that a mighty voice.  34Ascribe ye strength unto God: his excellency is over Israel, and his strength is in the clouds.  35O God, thou art terrible out of thy holy places: the God of Israel is he that giveth strength and power unto his people. Blessed be God.