This map plots the settings and references in The Road

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Page 20. " A log barn in a field with an advertisement in faded ten-foot letters across the roofslope. See Rock City. "
'See Rock City' barn on U.S. Highway 441, in Sevier County, Tennessee
GNU Free Documentation License'See Rock City' barn on U.S. Highway 441, in Sevier County, Tennessee - Credit: Scott Basford, April 2006

Though not the only advertisement or billboard mentioned in the book, this one is a solid clue to the book's setting, placing it firmly in the southeast US. Rock City is a tourist attraction, a natural rock formation on Lookout Mountain, near Chattanooga, Tennessee.