Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2354; U; en) Presto/2.8.119 320X240 LG VN530)
I think A & B are seperated geographically within the precinct. Either North & South, or East & West, but I'm not positive.
Each agency has their own way of assigning unit ID's, there is no real standard.
In Peoria, the first number is the shift 1-4, then the beat area 1-9, then the officer 1-9. George units are Sgt. Lincoln are Lts. Mary units are motor officers. If they have a 2 digit suffix number, they're Sgt's. If they have a 3 digit suffix number, they're officers. David are detectives. Paul are the Police Service Officers (PSO's) which are uniformed, unarmed civillian employees who assist with booking and transport of prisoners, crime and accident scene investigations, traffic control, report taking, records, etc. Park Rangers and Animal Control Officer's are PSO's, AC is the ID for animal control.
Glendale ID's are similar as far as patrol (up to 5-6 beats, not 9 like Peoria IIRC) and detectives. They call their PSO's Civillian Service Officers (CSO's), I'm not sure of their ID's.
Phoenix uses the precinct number 2-9 first, but on the air typically drop it, then the beat and officer number, followed by an alfa suffix (921G). Sgt's use the precinct number, their number, followed by a suffix. (92G would be 921G's Sgt.)
MCSO uses their district number 1-8 (Southeast, Southwest, Northwest, Northeast, Lake Patrol, Queen Creek, Fountain Hills and Mountain (formerly Parks & Trails) are the districts in order), followed by the beat and deputy number, then a suffix to indicate shift and whether a 1 or 2 deputy unit. A Mary suffix is a process server, usually on the Central TG, but I think I've heard them on West as well. A Paul prefix followed by a 3-4 digit number is a Posse member. I've also heard Constable units on the West TG, they may also be on East.