The radio codes used by law enforcement in the United States vary from one locality to the next, explains National Public Radio, but a list of common law enforcement codes is available at Colemer.org. However, many agencies no longer use the dispatch codes as of 2015.
The Colemer site lists the most common police call codes as well as those for military police and the Drug Enforcement Agency.
The terrorist events of Sept. 11, 2001 illustrated the problem of differing codes when local, state and federal law enforcement agencies were unable to effectively communicate with one another over the radio, explains NPR. This problem has led many law enforcement agencies to abandon radio codes altogether. As an alternative, they are adopting plain English for their radio communications. Because the meaning of the numerical codes is widely available, they no longer lend any secrecy to radio communications.
A 2005 Missouri incident illustrates the benefit of using plain English rather than radio codes, NPR reports. When an Independence, Missouri, police dispatcher received a radio report of a Missouri State Highway Patrol officer in a ditch with multiple gunshot wounds, she used plain English to advise the highway patrol of the incident. Had she not used plain English, the police department's 10-33 code, meaning an officer has been shot, would be interpreted by the highway patrol to indicate a traffic backup, and vital help would have been delayed.