Continuity mistake: When the nurse is giving Liam Nelson the address of the investigator, in one shot she's writing the note with her left hand, and in the next shot, she has the pen in her right hand.
Continuity mistake: In the scene when Liam Neeson wakes up from unconsciousness following his car accident, the nurse writes something on her notepad with her right hand, but in the next shot the pen has suddenly switched to her left hand as she puts it into her pocket.
Continuity mistake: The original taxi (with number) is parked outside Gina's apartment complex and they use it to escape, but it went into the river during the accident and Gina's taxi owner boss laments about it early in the movie.
Continuity mistake: The password needed to access Leo Bressler's hard drive, Umbellularia californica, is visible in the book. In the next shot 'umbellularia' is incorrectly typed into the password box as 'umbellurlaria', yet it gains access to the drive.
Answer: The 'OZ' sprayer is a very disturbed man who claims to be an artist but the courts think otherwise. You can found his OZ (which he claims to be read OLI!) everywhere in Berlin and Hamburg. It has absolutely nothing to do with the movie but you can't film a wide open scene in Berlin without taping it.