The glyphs for this episode spell out: REVEAL
The lock combination is 5-20-10, to which Walter says "I always use the same combination, but I can't remember the significance." The date of the season finale is May 20, 2010, or 5/20/10.
At the day care centre entrance, there are figures on the wall of a flower, seahorse, butterfly and hand, similar to what is shown during the breaks.
September walks in front of a large fire truck just as Broyles and the fringe team are arriving in front of the building from the alternate universe.
In the opening scene, Manhattan is spelled with only one 't' in the floating text.