Marco:
I’ve never seen any special markings on a West Side Lumber Co. car, fire or otherwise. In fact, West Side rolling stock usually only had a simple number, with no other markings. The locomotives were lettered for the WSLCo., using a special orange color.
Further afield, the large, mostly standard gauge logging railroads did frequently have lettering that showed the type of service for special cars. I remember seeing a fire car painted red and marked “Fire Service” or something similar. Can’t remember which railroad, but I think it was one in Washington State.
I see you have an oil burning 3 truck Shay. You might also consider devoting the tank car to servicing the oil burning Shays, and build a more typical round tank car for water / fire service. Those cars usually had a pump surrounded by hand railings on the top or on one end, along with some large amount of hose.
BTW, Nice model of the coffin tank!!
Is your rail painted? Or is it possibly the new Train Li plastic rail?
Happy RRing,
Jerry