I doubt that stenciling was done at the GM plant, more likely where ever the bed was added or maybe if the original purchaser was "corporate" it could be their inventory ID, a standard thing done with commercial buses and fleet trucks

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics