One of the people guarding Martin is reading the "Detective Comics" (now known as DC comics) April 1938 issue, which is one issue prior to Batman's first appearance.
A Maniax graffiti of the Jerome Cult can be seen when Penguin and the Riddler pass by a wall in the Narrows.
When Bruce and Selina are in the pawn shop, there is a green- and white-striped flag in the background. It is really the flag of the NYPD.