In the early years of motoring, federal, state, and local municipalities were sometimes loose about installing road signs, anything from distance to points of interest. Many automotive companies took it upon themselves to erect such signs. Goodrich Tires made "Goodrich Guide Posts," which were miles to destination signs, and U.S. Tires posted signs on the outskirts of towns telling the town's history. I believe these Shell signs fall under a similar category, of advising motorists of upcoming points of interest on the road, where there were no other signs to do so.
