Louis Sullivan was a titanic force in American architecture, influencing an entire generation of designers directly and indirectly. Among his many accomplishments was an ornamental style so unique and distinctive that it spawned an entire genre of imitative mass-produced catalog ornament. These terra cotta pieces show up on buildings all across Chicagoland.
Here's one particularly common design:
But there were many others.
They appear again and again on Chicago commercial buildings, adding a distinctly local note to otherwise forgettable architecture. They rather contradict Sullivan's own design philosophy, which considered building and ornament to be one unified, interrelated work of art, each custom-designed to fit the other and to serve the whole. These guys, by contrast, were just picking stuff out of a catalog. But hey, it's impressive stuff!
The term Sullivanesque comes from the book of the same name, which catalogs not only these shallow-but-pretty imitators, but also a whole school of design based directly on Sullivan's design style.
If you're not convinced by the organic-unifed-work-of-art argument, there's a place where you can compare a Sullivanesque building with an actual Sullivan design, in Lincoln Square. Right by the neighborhood's central plaza stands a fairly impressive bit of Sullivanesque, one of the few to actually make some attempt at integrating ornament and design.
But just a block south, the last built design of Sullivan's life - the Krause Music Store facade - blows its imitators completely off the map. There's simply no comparison.