When the Department introduced the ZIP (Zone Improvement Plan) code system in 1963, the public was reluctant to memorize and add numbers to mailing and return addresses. The Department began a nation-wide publicity campaign for the service, using posters, radio, and television advertisements, to enticing noted singer Ethel Merman to record a ZIP code song (which she sang to the tune of "Zip-a-dee-doo-dah").
Harold Wilcox, an art director working with American Telephone & Telegraph (AT&T) in New York City, created the symbol, whose original name was Mr. P.O. Zone. Renamed Mr. ZIP, the character was used to advertise the efficiency of the new service across the country. The speedy acronym of ZIP code service was no accident, and Mr. ZIP became the postal system’s mascot for quick mail delivery.
The Post Office Department initiated its Zoning Improvement Plan (ZIP) on July 1, 1963. The new ZIP code plan created a numerical representation of U.S. addresses to help speed mail processing. The new numbers direct mail through mechanized equipment in sorting centers. The five ZIP code numbers represent areas of the United States. The first digit indicates a geographical area of the country, beginning with zero in the northeastern states and ending with nine in the west. The next two digits indicate mail sorting centers near the final address. The last two digits represent post offices in small cities and postal zones in larger cities.
By the time four more digits were added to ZIP codes in 1983, postal equipment had evolved from mechanized machinery to automated machines using Optical Character Readers (OCRs) to read and process mail in sorting centers. Of the extra four digits, the first two indicate a delivery section (anything from a collection of blocks, streets or post offices boxes to a large building), and the last two bring the mail close to its final address.
Nancy A. Pope, National Postal Museum