Just before opening credits the camera pans down to a distant view of Manhattan. Just right of the World Trade Center is a fairly tall, oddly rounded skyscraper. That is the never-built Hotel Attraction, commissioned in 1908 and designed by Antoni Gaudi. Few people knew it had even been considered until certain documents were released in the 1950s.
When Peter regains consciousness in the room full of medical equipment, just as the "anesthesia" lights go out you hear three musical notes.
They're from the chorus of a song by George M. Cohan, entitled "Over There".
The glyphs in this episode spell out: WEAPON
The US map on Walternate's wall is of the contiguous states only and much of the west coast south of the state of Oregon is missing, including all of western California. Clearly, in that universe the San Andreas fault had given way.
The evidently abandoned theatre where Walter and company jump to the alternate universe is the very much still active Orpheum Theatre in Vancouver, one of the three most important venues for live performances in the city.