That streaking comes from the nails in the nailing fins, as a rule. I'de be more worried about the water that satys behing the siding and often does damage there. You might want to check behind the sidng to see how the window is flashed.
My siding has a hole in the bottom edge to allow the water out, from on top of the flashing. You can check out window flashing on the site in my signature.
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