According to Einvestigator.com, there is no truly universal or official set of 10 codes, and the meanings of a particular signals can vary between one police jurisdiction and another.
10-23: Stand by on this frequency (also stands for “on scene” in some areas)
Ten-codes, 10-codes, police codes and sometimes “police scanner codes” are signals that are used by law enforcement and government agencies in two-way voice radio communication as numeric code words for frequently used messages. Ten-codes are also used by private citizens in Citizen’s Band (CB) radio transmissions.
10 codes originated in the United States law enforcement community prior to the Second World War. The first set of 10-codes was published by the Association of Public-Safety Communications Officials in 1940. These radio signals were invented to help reduce the use of speech on the police radio.
In addition, they add a certain amount of privacy to the transmissions, as one must know the meaning of the signals to understand the discussion. Use of the police radio codes was expanded in 1974 by the Association of Public Safety Communication Officials (APCO) to make them more brief and standardize message traffic.