My old forces callsign used to be easy. Division + Team + Driver Training (area car, response or basic) + Sequential number. So it would be something like E4Y1 for the area car, team 4 for E division.

Then they moved in line with a couple of other forces so now it's Force + Division + Team + personal callsign based on rank and then driver training (it only changes if the driver is the area car). So that same callsign is now NE420.

My new force uses similar styles of callsign but the last two numbers are a jumbled mess, aside from rank, there is no indication as to who is a basic or response driver, we don't have area cars and multiple divisions have the same letters so it's a bit of a cluster...