There are a couple of different methods used to identify a unit over the air...
1) Precinct number followed by precinct sector letter (i.e.: 33A, 44P - oftentimes clipped to one number only...3A, 4P)
2) Car number (anywhere from one to four digits)
3) Function (for example: Precinct number + "H.O.W." = car assigned to pay special attention to Houses of Worship during high holidays)
4) Note that specialized units use assorted methods.
- Highway units ID with S (for sector) + Highway Unit number (1, 2, 3, or 5) + post number (i.e.: S101, S206, etc - the S is often dropped)
- Emergency Service units ID with unit letter + Squad number (i.e.: A1, B2, Truck 10)
- Some plainclothes units ID with code names (i.e.: Tom Alpha)
- Precinct Detective Squad detectives ID as "# (Precinct #) Squad"
- Detectives assigned to Accident Investigation Squads ID as "# (Highway Patrol Unit #) Follow-Up"
- Detectives assigned to Patrol Borough Anti-Crime Units ID as "__ (fill in Borough) Crime"
- Detectives assigned to other specialized units will ID with whatever car number they are in (anywhere from 1 to 4 digits) or using code names.
By the way, I forgot to mention in my post above that Housing Bureau units - who are also dispatched over Zone channels - ID as "Housing Posts #" or car numbers from 9100 up. I will refer readers to page 23 of Edition 7 of Scanner Master's NY Metro / Northern NJ Comm Guide for an explaination of the Transit Bureau's radio ID scheme on their stand alone radio system.