This is Fringe's 100th episode.
The 'inbetween picture' of the skeleton hand has 5 fingers and a thumb. In the final episode, when Olivia and Peter are going through the building with observers and loyalists which they attacked with chemicals, there is a bloody hand print on the wall. This hand print also has 5 fingers and a thumb.
The coded glyphs at the commercial break spell CLOSE.
The apartment number where September went to meet December was 513. It is the episode number.
In a twist on the ' green, green, green, red' pattern of lights seen on previous episodes, when Peter (Joshua Jackson) shorts out the keypad, the light flashes 'red, red, red, green.'