The glyph/code spells out STILL.

Olivia: What the hell are you doing?
Walter: Sleeping. One syringe has sodium thiopental...
Olivia: Well, that sounds...
Walter: It's a barbiturate, yes.
Olivia: I was going to say "dangerous."

Walter: Seeing this man has brought up many things I've tried to forget. That night at the lake, you begged me to stop, but I couldn't. I couldn't watch Peter die, not again. I couldn't stand by and do nothing.
Nina: Walter...
Walter: I've hated you. For 25 years, I hated you. Had you not been there, the vial wouldn't have been broken, and I would've healed Peter on the Other Side. he wouldn't' have fallen through the ice. I blamed you for the death of my son. I blamed you. i couldn't live with myself... because you were right. I'd crossed the line. For the sake of one life, I destroyed two worlds. And over the years, I've come to terms with the fact that I deserve to be punished... to suffer.
Nina: No. Walter, you're not that man anymore. I've watched you. working with the Fringe Division, you've done everything in your power to heal the damage.
Walter: I saw him, Nina... the man. I saw my boy in that man's eyes. The way he looked that night in the ice... floating away from me. God help me, I... saw the eyes of my boy in a man's face. That filled me with... indescribable joy. but I don't deserve joy. For anyone else, this would be received as a miracle--to get a glimpse of their dead son. why should I be rewarded for what I've done?
Nina: Because maybe you've suffered enough. No, I can't explain it, Walter. I don't know why he's here, I don't know where he's came form. But maybe you've just been given a second chance.

Walter: Every day... for the past 25 years... I tried to imagine what you would like as a man... my son. But I don’t deserve this. I don’t deserve you. I realize now this was my punishment. You were sent to tempt me, to see if I would repeat the mistakes of the past. You shouldn’t be here.
Peter: Walter, no.
Walter: Wherever you came from, however you got here, it doesn’t matter. I can’t help you.
Peter: Walter, you don’t understand.
Walter: I tried to help a boy, a version of my son, 25 years ago. But that boy was never my son... and neither are you.

The Observer can be seen in the background as Olivia arrives at Karen's house.