A quick Google search indicates it was in business from about 1915 to 1943. GM was a majority owner from about 1923 on and sold it's Yellow Division to Yellow Coach. They built taxicabs and motor coaches and then it was absorbed by the new GMC Truck and Coach in 43'. Some of the production numbers are surprising high.
My best guestimate or SWAG is that Yellow was the upfitter for the front drive axle conversion in 1940. Many are surprised to learn that Detroit has a long history of aftermarket or specialty upfitter involvement and in this instance actually owned one. There are likely others who have direct knowledge of the Yellow history but a lot can be gained by a simple search.
If your truck is in good condition or is worth repairing I'd say it is a rarity if in fact not valuable. So give us some photos new guy..you know how we love those pictures.
