Hard to tell. Are the lines damp? If not, the staining could be from a lot of things...even staining before the plywood was installed. What you should do is check on this again immediately after the next hard rain to see if anything is damp or leaking.

Or test it with a friend. Stand inside and have them outside with a garden hose and look for leaks.

How do you know those marks weren't there before?

do you have ridge venting?

had a blowing rain prior to the pics?

take another pic where the water starts,

higher up on the roof decking.