The "Tulip Food Store" signage in '6B' foreshadows Olivia and Peter meeting for the first time in a field of tulips in 'Subject 13'.
The periodic table of elements in the Jacksonville daycare center in 'Subject 13' displays the element Osmium, the element featured in 'Os'.
WALTER: "Aha. The beguiling Olivia Dunham beguiles."
OLIVIA: "My stepfather did this. He hits me. That's when I crossed over to the other universe. Look [as she hands Walternate a sketch pad with "Olivia" on it]. That's where I saw the blimps. Just like you said. They were in the sky in the other universe. Can you make him stop hitting me?"
WALTER: "Before you go. I want you to understand that this girl is very special to me. And if anything harmful should happen to her, anything to frighten her or make her uncomfortable in the least, I will not hesitate to inform social services. In which case I have certain government friends who can ensure that you'd be facing significant troubles for yourself. Do you understand me?"