Sometimes called the "ten codes", these are a shorthand, most often used by police officers, to quickly and efficiently communicate, with a low chance of misunderstanding. The codes are:

Source: Pocket Ref, Second Edition, Thomas J. Glover, Sequioa Publishing

These "10-Codes" are different for most police agencies.
Here are a few from the Fairfax County, Virginia Police Department.

10-3 - All units stop transmitting
10-4 - Acknowledgement, Message recieved
10-6 - Unit Busy
10-9 - Re-Transmit
10-15 - Suspect / person in custody
10-17 - Warrent Service
10-26 - Backup needed
10-33 - Emergency
10-98 - In Service - Report to follow
10-99 - In Service - No Report

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