For Yolo County:
Law enforcement units generally use the following format: number-letter-number
The first number designates the agency:
1 - Yolo County Sheriff
2 - Woodland PD
3 - Davis PD
4 - UC Davis PD
5 - Winters PD
6 - West Sacramento PD
7 - Yolo County District Attorney Investigators
8 - YONET
9 - Yolo County Arson or Bomb Squad (I think...)
The meaning of the letter designator varies by agency, but generally D = day shift, S = swing shift (except in Davis, where it is sergeants), G = graveyard, etc. etc. Enough listening will usually let you figure out the letter meanings.
The last number is either the badge number (Davis PD), the # of units on the shift such as Sam 1 thru Sam 4 (Woodland, West Sac, Winters), or the beat and # of units on the beat such as 1 George 42, second unit assigned to beat four (Yolo SO).
Note that units often omit (or don't key up fast enough) their agency identifier when transmitting.
You'll also occasionally hear state probation officers on various Yolo channels, they identify as "Silver ##", or sometimes CHP "47-##" or State Fish & Game units.
