From the National Postal Museum:
Introduced in 1963, the U.S. Postal Service’s “Zone Improvement Plan” revolutionized how mail was processed. Using numbers to stand for regions, cities, post offices or neighborhoods made it easier sort the mail by machine or by hand. To make this possible, the public had to adopt the habit of including designated numbers with their mailing addresses.
The “Mr. ZIP” character was introduced in 1964 as a friendly reminder to use ZIP codes. While Mr. ZIP has been a well-known part of postal history for decades, only recently has the existence of a Mrs. ZIP been confirmed. In 2008, National Postal Museum curators came upon this “Mrs. ZIP.” There is no known documentation of Mrs. ZIP, but the museum staff believes she may have been used in local parades or at New York City’s old main post office where she was discovered.
The Smithsonian displayed the images of the ZIP’s at the recently concluded NPF.