Over the summer, CBS News’s “Sunday Morning” did a piece celebrating the anniversary of the U.S. Zip code. A commercial explaining how to use the Zip code showed a sample letter addressed to “Anywhere, USA.” The return address was to Mr. ZIP, with a real address: 3374 N. Dinwiddie St., Arlington, VA 22207. It caught my eye because the Zip code identified the neighborhood where I grew up in Arlington. I’m guessing it’s the address of the postal inspector’s house or the creator of the Zip code. Do you have any ideas?

Mary Haffey, McLean, Va.

It could be said that the Zip code was the mark of Cain: D. Jamison Cain, that is, a Post Office Department executive who helped persuade the American public to use the “zone improvement plan” when it was introduced on July 1, 1963.

And where was Cain living when the code debuted? With his family at 3374 N. Dinwiddie St.

Cain was from South Carolina, a journalist who worked at newspapers in Columbia, Charleston and Camden. In 1955, he took a job in Washington as the bureau chief of the Sims News Bureau, which served 40 media outlets in the South. In 1961, he was appointed to serve under the postmaster general.

The need for some way to efficiently sort an increasing number of letters and parcels had become more urgent during World War II, when inexperienced workers were being hired to replace clerks who had been conscripted for the war. In 1943, the Post Office Department, then a Cabinet-level agency, introduced two-digit sorting codes for some large cities, including Washington.

Philadelphia Postal Inspector Robert Moon thought the system could be expanded to cover the entire country and made more precise. J. Edward Day, John F. Kennedy’s postmaster general, approved the idea.

The new plan employed a five-digit code. The first number represented one of 10 national service areas. The second referred to a subdivision of that area. The third digit represented the post office that handled that specific address. And the last two digits denoted the station from which that mail would be delivered.

Postal executives in West Germany — which had rolled out something similar — told their U.S. counterparts that the key to getting public acceptance was to heavily promote the new system’s use.

That’s where Cain came in. Many an ex-newspaperman make a good pitchman. Cain came up with the phrase “zone improvement plan” and dubbed the mascot “Mr. ZIP.”

You can get a sense of Cain’s vigor from a three-page memo he sent to his postal colleagues on April 22, 1963, as the department moved to Phase II of its plan. His 37 action items included making sure a Zip code fact sheet was up to date, ordering life-size cutouts of Mr. ZIP for postmasters to set up in their post offices, and securing copyright on the Disney song “Zip-a-Dee-Doo-Dah” so its lyrics could be rewritten for use in promoting the Zip code. (A “fifth of good booze” was promised to whoever came up with the best parody.)

Some of the publicity materials included sample envelopes addressed to show the Zip code in use. And on some of those, the return address was 3374 N. Dinwiddie St. in Arlington.

“It was like so many of the houses in Arlington: a two-story brick Colonial,” said Cain’s son David, who grew up there with his brothers.

It seems amazing now that an actual address was used. Today, David said, “You’d get sued in a heartbeat.”

Perhaps Jamison Cain favored the specificity of a real address, as opposed to a generic, fictitious “Ourtown” or “Anywhere, USA.”

That return address also seemed to make Mr. ZIP real.

“I was really pretty sure that he was the model for Mr. ZIP,” David said of his dad. “He was a skinny guy with a round face. His ears stuck out.”

But as Cain told his son — chagrined that the boy thought he resembled a childlike scrawl — the figure actually predated the Zip code. The character was designed by an ad agency artist named Harold Wilcox for Chase Manhattan Bank to promote its banking-by-mail campaign. AT&T acquired the design, then ceded it to the Post Office Department to use for free.

A Cain family story describes Jamison’s mother’s reaction the first time she laid eyes on Mr. ZIP. “What is that ugly little thing?” she said.

“Mother,” Jamison replied, “I will assure you that before I am through with this ugly little thing, everybody in this country is going to know who Mr. ZIP is.”

Mr. ZIP’s ubiquity worked. By the time the figure was retired in 1983, nearly 100 percent of the mail that crisscrossed the country used the Zip code.

Jamison Cain died in 2010. The Zip code lives on.

(A tip of the Answer Man hat to Jenny Lynch, a historian at the U.S. Postal Service, the successor to the Post Office Department.)

Questions, please!

Curious about something in our area? Send your question to answerman@washpost.com.

For previous columns, visit washingtonpost.com/john-kelly.