Mark's Jesus eschews signs, so it makes sense that Mark omits any mention of Jesus' nativity such as Matthew and Luke have relying on Isaiah

 

 The virgin birth, according to Isaiah, is a sign, after all.

Therefore the Lord himself shall give you a sign [σημεῖον -- LXX]; Behold, a virgin [παρθένος -- LXX] shall conceive, and bear a son, and shall call his name Immanuel. 

-- Isaiah 7:14

Behold, a virgin [παρθένος] shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us.  

-- Matthew 1:23

For unto you is born this day in the city of David a Saviour, which is Christ the Lord. And this shall be a sign [σημεῖον] unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger.

-- Luke 2:11f.

There shall no sign [σημεῖον] be given unto this generation.

-- Mark 8:12

 

Jesus did not "lay aside his divinity" at the incarnation as Bill Johnson says, but is already "from the Holy Ghost" in his mother's womb and becomes "God with us"

A heretic of Christianity is discussed here who teaches that Jesus laid aside his divinity in the incarnation and performed his ministry entirely according to his human nature by the subsequent gift of the Holy Spirit received at his baptism by John, in order to pave the way and make it possible for his followers to receive the same, and do the same and greater things.

Utter nonsense, of course, which the author of Matthew would not have accepted:

Now the birth of Jesus Christ took place in this way. When his mother Mary had been betrothed to Joseph, before they came together she was found to be with child from the Holy Spirit. ... But as he considered these things, behold, an angel of the Lord appeared to him in a dream, saying, "Joseph, son of David, do not fear to take Mary as your wife, for that which is conceived in her is from the Holy Spirit. ... "Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel" (which means, God with us).

-- Matthew 1:18, 20, 23

Some Evidence Of Outsiders' Dim View Of Jesus' Origins

Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost.

Then Joseph her husband, being a just [man], and not willing to make her a publick example, was minded to put her away privily.

-- Mt.1:18-19

I speak that which I have seen with my Father: and ye do that which ye have seen with your father.

They answered and said unto him, Abraham is our father. Jesus saith unto them, If ye were Abraham's children, ye would do the works of Abraham.

But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham.

Ye do the deeds of your father. Then said they to him, We be not born of fornication; we have one Father, [even] God.

-- Jn.8:38-41