In the 1908-1910 era "street signs" were basically painted letters stenciled onto the poles that were usually on the corners in neighborhoods. Street signs started popping up after that period. Here is a photo I saved from e-bay of men that took part in breaking up the 1919 Chicago race riots. Note the 63rd & Racine street sign.
During WWII most of the street signs were taken down for metal drives to support the war effort. They started to come back in the late 1940s and early 1950s. In the late 1970s early 1980s the yellow signs were replaced with the modern green signs. The city of Chicago sold signs to residents which is why so many survive.