The name of Michael Madsen's character was "Benjamin Walker." This name is very similar to the name, "Benjamin Barker," which was "Sweeney Todd's" name, before he changed it. Both characters were on missions of vengeance, concerning a wife and child. Also, Len Cariou, who plays the "patriarch" of the Reagan family, originated the role of "Sweeney Todd" (the musical) on Broadway.
All the cops, including Renzulli and Jamie Reagan, are wearing official "City of New York" patches, and vehicles have the correct serif-style NYPD door logos.
The serial number of Blake's sidearm is KKT 345, which, according to the manufacturer's numbering system, means that it is a Glock model 19 that was built in October of 2006.