Called a "cachet," it's limited edition stamped envelope and features a cancellation stamp with the zip code of McCormick Place: 60616.
There's also an enlargement of the 1952 3-cent NATO postage stamp.
This collectible will sell for $5 and is available at these stations: Cardiss Collins Postal Store (Main Post Office), 433 W. Harrison; Station E, 100 W. Randolph; Loop Station, 211 S. Clark; Wacker Drive (Wills Tower), 233 S. Wacker Drive; and Streeterville, 355 E. Ohio St.
