What types of signs are given by the "lights in the expanse of the heavens"? On the fourth day, God created lights in the expanse of the heavens for "signs", among other things.


  Then God said, “Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years. Genesis 1:14 NASB


I understand the astrology seems to be forbidden in the Scriptures:


  You shall not eat anything with the blood, nor practice divination or soothsaying.  Leviticus 19:26 NASB.


So, what specific signs are referred to here?
There is a definite difference between trying to foretell an unknown future and seeing things unfold and knowing what's going on.  I don't have to be a meteorologist to know that when dark clouds start gathering overhead there's a chance it might rain.

A good representation of this is in Revelation:

"I watched as he opened the sixth seal. There was a great earthquake. The sun turned black like sackcloth made of goat hair, the whole moon turned blood red, and the stars in the sky fell to earth, as figs drop from a fig tree when shaken by a strong wind. The heavens receded like a scroll being rolled up, and every mountain and island was removed from its place.  Then the kings of the earth, the princes, the generals, the rich, the mighty, and everyone else, both slave and free, hid in caves and among the rocks of the mountains. They called to the mountains and the rocks, 'Fall on us and hide us from the face of him who sits on the throne and from the wrath of the Lamb! For the great day of their wrath has come, and who can withstand it?'" (Rev 6:12-18 NIV)

Having read this, you would not have to be an astrologer to realize that when the sun goes black, the moon turns blood red and heavenly bodies start crashing to the ground that the sixth trumpet has sounded.  It's already been foretold in the Bible.  You're just recognizing the signs when they come to pass.

Seeing a sign for what it is isn't the same as trying to divine the future.  Divination is trying to see the unknown.  We've already been told in the Bible what to watch for.

We are to be watchful and alert.  Jesus said there would be signs and that "when these things begin to take place, stand up and lift up your heads, because your redemption is drawing near." (Luke 21:7-31 NIV)