In my department, the engines and trucks are numbered according to the station they are assigned 1-12. When the 1st out unit is down for maintenance a reserve unit is used it has magnetic numbers applied to identify what station it is working for that time period. This is for Eugene Fire. I started working at a rural dept where the numbers identified the type of unit like mentioned above.
219= Station 2 (CGFdept) 1st out ambulance
211= Station 2 (CGFdept) 1st out pumper
321= Station 3 (JCFdept) 2nd out pumper
The first number signified which departments had been around the longest, in most cases.
