The Observer can be walking past the Rosencrantz building, right at the beginning of the episode.
Hidden Glyph: I didn't see any hidden Fringe symbols in this episode. It may not be an "every episode" Easter egg, like the Observer or Next Episode Clues. Or maybe I just missed it... if you find something, let me know!
Next Episode Clue: In the last episode "Immortality", the license plate of the second victim is APT6B. In this episode, Alice Merchant lived in Apt 6B, which is also the title of the episode.
Glyphs code in the Fringe episode 6B spelled out HEARTS.
In fact, in the final glyph of the "glyph code", the standard yellow "firefly" was replaced by a heart.
Green, Green, Green, Red: The lights on the Amber-releasing device light up Green, Green, Green, Red, like the amnesia-inducing devices in The Equation.
Some other interesting screenshots from 6B:
Tulips: There was a recurring theme of tulips throughout the episode. Was the a reference to the love story in White Tulip, or possibly the Next Episode Clue for Subject 13?
Rosencrantz and Guildenstern Are Dead". According to Wikipedia:
The play opens with Rosencrantz and Guildenstern betting on coin flips. Rosencrantz, who bets heads each time, wins ninety-two flips in a row. The extreme unlikeliness of this event according to the laws of probability leads Guildenstern to suggest that they may be 'within un-, sub- or supernatural forces'. The reader learns why they are where they are: the King has sent for them. Guildenstern theorizes on the nature of reality, focusing on how an event becomes increasingly real as more people witness it.
Schrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The thought experiment presents a cat that might be alive or dead, depending on an earlier random event. In the course of developing this experiment, he coined the term Verschränkung (entanglement).
The booze that Olivia brings over is labeled "Kentucky Straight Bourbon", but anyone who lives in KY (like me) can tell you that the distinctive bottle is the super-premium small batch bourbon Woodford Reserve. Mmmm. It's too bad they didn't do an actual product placement.
For the Polivia "shippers"!