Not a mistake, but worth looking for. Roman Strauss's mansion in the film is the same house used as Wayne Manor in the Batman TV series, with Adam West.

When the audience first meets Mike Church, he's sitting in his car, which is parked on the wrong side of the street. While most people believe this is because Kenneth Branagh is from the United Kingdom (where they drive on the opposite side of the road), it is actually because behind him are a number of skyscrapers that he, as the director, wanted included in the background.

The serial number on Roman Strauss' prison uniform, 25101415, stands for "25 October 1415." This was the date of the Battle of Agincourt (fought by Henry V) - the subject of director/star Kenneth Branagh's previous film, "Henry V."