Those are the status numbers of the vehicles.
Here is a list of the used status numbers in Mission Chief:
Status 1: Free on Radio 
Status 2: Free on Station  
Status 3: On its way to mission 
Status 4: At mission 
Status 5: Requesting transport  
Status 6: Not ready for duty 
Status 7: Transporting person
Status 9: Awaiting vehicle to tow