One of the most obvious symptoms of an impending migraine would be the visual aura. This was posted on the you-tube as a demonstration of what a migraine aura looks like:
Of course, the visual aura takes on infinite possibilities. And with the type shown here, it can be negative… as in more a deep blue and black, rather than white. And let’s not forget the speckled dots of light that just linger, the flashing in the side vision and the raining sparkles.
Also, auras are not all visual. They can be phantom smells, auditory hallucinations, tactile like numbness and tingling, as well as things like transitory aphasia.