This symbology, derived from the RM4SCC system used by the British Royal Mail, uses a series of bars, each of which can individually have one of four possible states, to encode information used in automated sortation and delivery onto each piece of mail.
The police call in Professor Langford Fife (a pastiche of both Robert Langdon from the book and Barney Fife from The Andy Griffith Show), a professor of symbology at a local community college, to help them solve the mystery.