In case you were expecting the 1980s rock band!
REO was started by R.E. Olds in 1905 (his former company, in which he was no longer involved, became Oldsmobile), building cars and trucks until 1975. The Speed Wagon was a light truck – the precursor of today's pickup truck – made after 1910 and continuing for some years. Manufacture of cars ceased in 1936 after the worst years of the depression and competition forced the company to concentrate on trucks. The Speed Wagon had several forms including fire trucks.
This looks like the 1917 model Speed Wagon which was a 3.25 ton vehicle with canvas top, canvas roll-up sides and snap closure isinglass doors, here shown tied back. It cost $1125. The name is painted on the ends of the gas tank which is mounted behind and below the windshield where the dashboard would normally be.
The truck in this photo is carrying both bottled milk and milk in cans; since there is no company name visible it may have supplied products to retail food stores rather than home delivery, but who knows. Why the spare mount only has a rim instead of a complete tire is a good question – what good would that be if you had a flat? Note that the rear tires have tread for traction but the front tires are smooth. The REO name was pronounced as a single syllable even though it was based on Olds' initials (the Olds name was never used for this company because of conflict with the other Olds company name)