This truck as an example:
L is for city/region
S is for volunteer unit

Numbering goes when there´s used this two number system:
First number points for firehouse. In this truck it´s 2, so it´s second firehouse in that area
Second number sings for type of unit.

1 - Fire/Rescue unit
2 - Fire/Rescue unit "second wave"
3 - Tanker
4 - fire extinguishing powder or foam unit
5 - Heavy Rescue
6 - Aerial unit
7 - Support unit
8 - Flatbed truck with changeable containers. HazMat,Heavy rescue etc.
9 - Ambulance
0 - Mobile command center

In three number system:
Like in Helsinki, numbers goes like: H Region,Unit type,Firehouse

And S is still for Vollies.
Example of numbering with three numbers
Helsinki City. Volunteer fire/rescue unit HS 512, Region 5, unit 1, firehouse 2. Pukinmaen vpk

There is Chief´s car numbering:
Single number with letter of city/region
1 - Captain
2- Head of fire inspectors/ Fire chief on duty
3- Liutenant on duty
4- Head of ambulance services, most times doctor onboard
5-9 Fire inspectors