In the Jen Heyward Tumblr Blog, which is proven to be part of the canon of the “S” story, we have discovered several clues. Here is another that needs more work. Perhaps you can find the source of the tantalizing text teasing us from beneath the spiral notebook in the photo below (the arrows are added to highlight the text).
Here are enlargements of the two sections. If you figure out the words and, more importantly, the source from which they come, let me know by email or in the comments and I’ll add your discovery and credit you. Good luck!