Centerville has a large collection of stone buildings, and many of the hides are in the heart of the architectural preservation district. The hides aren't anything special...but the places they take you to (and past!) are notable. What's so great about Centerville? The city has the largest collection of early stone houses in the state of Ohio. Many are listed in the National Register of Historic Places. That's what the sign says.
The cache is no longer hidden in the sign post. Although the old container is forever at the bottom of the shaft, it is no longer the official container. Read the hint. You're looking for a plastic waterproof matchstick container.
For a full list (with pictures & descriptions) of Centerville's Stone Buildings vist the Centerville Historical Society's webpage.