PAINTED SIGN & GRAIN ELEVATORS (Lincoln Highway Calamus IA)
This sign appears on a metal utility pole and guides westbound traffic around yet another jog in the old highway. Another arrow is out of sight in a lower blue band, pointing the other way for eastbound drivers.
Technically, the Lincoln Highway ceased to exist in 1926 when the numbered US highway system was adopted. However the name continued in use for years. Signs like these could be original, but repainted. It's impossible to determine.