Auto service cars were often used in other services. Both temporarily
and long term ... and then, later in the life of a car such as this one it
probably didn't see a lot of auto service assignments since newer/better
cars for the purpose would be introduced.
However, I think they would have retained their "Automobile" lettering
unless they needed to be repainted.
If you have a picture of this particular car that does not have "Automobile"
on it ... then you can use it anywhere you want! Otherwise you might
want to consider adding the auto lettering it and heavily weathering that
part to show it is in different service now ... ??? (It's old, weathered, and
being used for general purpose needs now.) Then again, if your YM
(wearing their car clerk hat) don't seem to pay much attention to stuff
like that you don't have to worry, do you?