My brakes were replaced about 2 months ago, rotors were resurfaced and some new pads were put on. The rotors were extremely noisy and left this dark stripe on the middle of the rotor. I was concerned with it, but because the car is a daily driver it went away after a week or so. Now, fast forward, I was doing some spirited driving on some back roads the other night, and the next morning I noticed the stripe came back along with a screech every time I tap the brakes. What is this? and how did it happen?

Here is a picture to that shows the dark stripe in the middle of the rotor.

 

Its most likely a heat mark, and it doesnt look like its the full width of the pad. Your pad may be hitting the rotor unevenly which can also explain a squeak. Not too much of a solution here except changing pads and redoing the rotors again if they are not too thin.

I dont suppose you changed your pads when you redid the rotors last time?