When Sierra is in Sato/Saito's office, and sits at the desk, the computer screen shows the letters "NSA" mirrored. The film has obviously been flopped for one reason or another.
Sierra acting as a spy impersonates a worker. When she first arrives in the building a guard scans her card revealing the name "A. Saito." Later Sierra enters the worker's office with a name placard clearly labeled "Ms. Sato" (a guard also refers to her as "Ms. Sato").
At the end of the episode when the mole fires the gun, the victim's blood is splattered behind them onto the glass indicating an exit wound on the back victim. Later we see the back of the victim with no blood or exit point on either their back or on the back of their shirt.
In the train scene, where Sierra takes over A. Saito's identity, right after Sierra takes a picture of Saito's eye, you can see her blinking even though moments before Saito was knocked out by Sierra.
When Sierra's ID is scanned by the NSA guard as she enters the building, her profile shows no ID #, while the previous employee reads 'ID #: 9476339473993'. Surely the guard would have found this omission suspicious, yet he lets her through without incident.
Sierra, imprinted as a spy, infiltrates the NSA. When she is making her escape and being chased by security guards she discards the wig she has been wearing. As the wig was in contact with her hair and skin it would likely contain DNA traces. This might allow the NSA to identify Sierra's true identity.