Police codes such as 10-8 and 10-4 are commonly used to communicate information, according to About.com. Additionally, 4, 13 and 0 are regularly used police signals. Police in California use what are known as "hundred" codes such as "four-five-nine" or "one-eight-seven" to provide a call description.
The status of a situation or an officer is commonly communicated with the use of a 10-code, explains About.com. A 10-8 code is used by a service unit or an officer who is ready to accept a call. Additionally, another use of a 10-8 code is in a conversation when describing a suspect who has gotten away. To describe the location of an officer or a situation, a 10-20 code is used. To provide an affirmative response and to indicate things are fine, an officer uses a 10-4 code. A car accident is described by using the signal 4, a signal 0 indicates a person has a weapon, and a call involving a stolen vehicle is expressed by using a signal 10.
Police signals and codes are used for quickly transferring information or a message to other members of the force, states About.com. Using codes and signals as a means of communication allows a police officer to better focus on his situation and saves time in transferring a message. However, codes and signals are not used to prevent the public from understanding police conversation or messages.