Agent Marshall Flinkman: Syd, this guy buried you alive.
Sydney: Yeah, but he cheated, he hit me with a car first.
In the episode where Sydney is supposed to be in Helsinki, there are visible skyscrapers in the background. There are no skyscrapers in Helsinki.
Throughout the show, the number 47 appears many times. There are multiple room 47's (where Syd found the Circumference in season 1 and the room in her memories from season 3, among others.), there are 47 Rambaldi artifacts, and page 47 of the Rambaldi manuscript was the page that had Sydney's picture on it.