With APD/TCSO/AFD/EMS, their dispatch UID's are generally the same as they utilize the same consoles to dispatch. Generally starting with a 1055XXXX.
With APD, their UIDs on their portables are their Employee ID's ("AP's" for APD)/Badge ID (which we dont call them that here). Generally their "Call Sign" i.e. Adam 101 will stay the same unless they move to a different unit. So if they are off duty working a side job doing whatever, they will always key up "Adam 101".
Their vehicle UIDs are the last 4 of the vehicle they are driving. So for example if you are on the road and you see a marked unit that has the numbers 9345 on it, if that officer keys up his mobile you will see UID XXXX9345.
The Sheriffs office is just a little different. I have not yet been able to track how their mobiles are assigned, but their portables are the same as APD, Employee ID. Their patrol call signs can change but other units besides that stay the same. I.E. "Central 94" (Major Crimes) will always key up as "Central 94" unless they move to a different unit. "5B10" (patrol) may be a different person one day as the person that usually covers that sector/district has to cover a different one. But primarily patrol generally stay within the same sector/district.
If a non-specialized unit is working off duty, they just identify as their Employee ID, i.e. "3044" would just be employee 3044.