The windscreen has cracked. Normally this happens in flight, I doubt it happened because of following a 747 (possible, though, I suppose). In the Dash-8 we had this happen a lot. It was due to an accumulation of water in the frame under the window, which would freeze at altitude and crack the windscreen. We put in drains in the frame, and the cracking stopped.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.