800,
The formula is rather simple. The units IDs as the precinct number followed by the assigned patrol sector. Examples include 1A, 5B, 7C, 120A, 122D, 123P. Oftentimes, on radio zone channels, the first digit(s) are dropped in multi-digit precinct designations (i.e. 3A instead of 33A, 2E, or 22E, instead of 122E). Units assigned to cover multiple sectors ID only has the alphabetic first sector (i.e. 28BCD will only go over the air as 28B).
Units that are not assigned to patrol sectors will identify in the clear. Examples include 13 Special Operations Lieutenant (or SOL or Special Ops), 9HOW for House of Worship car, 120 Beat 1 (a community policing post), 19 Training Sargeant, 23 Critical Response Vehicle (CRV, or just plain Critical, the car designated for availablity for citywide emergencies), 24IRT (IMPACT Response Team), 34 Crime (the anti-crime [plainclothes] team)...there are way too many to list. Did you have a specific ID in mind that you had a question about?
SCANdal