Factual error: In the last scene the ICE Train is leaving the station eastbound. It is not possible to enter these trains at the central station because all eastbound trains end in Berlin and have only one station left (Berlin Ostbahnhof). Every ICE leaving Berlin is going in the other (westbound) direction.
Factual error: Jurgen takes the cyanide out of a coffee tin. He mentions he has had it for years since his time in the Stasi. However, in fact potassium reacts with carbon dioxide to form a harmless compound over time: to prevent this it must be sealed in an airtight container, which a coffee tin most certainly is not.
Factual error: Liam Neeson is holding a Rolex Deepsea marked "EH to MH 7.18.06." The watch was released in 2008.
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.