Mary Martin thumbed through a stack of postcards.
When she got to a card that depicted a building at Aberdeen Proving Ground during World War II, she flipped it over and read the words scrawled on the back.
"This one is a note from a boy to his mom as he went to Jacksonville, Fla., for training during World War II," said Martin, 41. "I love reading the notes that tell what happened here, or what people from a century ago thought about this area."
Martin was perusing postcards -- from her collection of more than 10 million -- to make display boards depicting locations throughout the county, for the Spring Chesapeake Postcard Fair that she is hosting in Havre de Grace on April 4 and April 5.
A well known deltiologist, Martin has coordinated the show that will include about 30 dealers from 12 states, and more than 1,000 collectors from around the world.
"Our show is one of the largest in the country," said Martin, who also promotes shows in Orlando; Memphis; York, Pa; and New York. "Dealers love it because it's a break from the large cities. And collectors love it because it's so close to the train station in Aberdeen. They can just take the train from big cities."
Martin's reputation in the postcard arena has also helped to make Havre de Grace a postcard mecca for collectors. During the past five years, Martin said she has seen a tremendous growth in demand for postcards.
"I can't keep up with all the requests I get for postcards," said Martin, who took over the postcard business that her mother, also named Mary Martin, started. "I get hundreds every week. People call me, write or e-mail looking for postcards."
Collecting in general is increasing, but postcards appeal to everyone, she said. Recently, Martin attended a national coin show and attendance was more than 10,000, she said. Although fewer people show up for the postcard shows, anyone can be persuaded to buy a postcard, she said.
"There are a lot of people who collect coins, but it's easier to interest a noncollector in postcards," Martin said. "I can bring anyone into a postcard show, and they will buy a card before they leave. You can't talk someone without a collection into buying coins."
The most popular postcard subjects are political and social history, women's rights, losers in presidential elections, and United States hangings, she said. Some cards that show U.S. hangings can sell for as much as $4,000 each, she said.
Most of the requests she receives from people are nostalgic, hometown views, she said.
"People are looking for a card of the church their grandmother was married in," Martin said. "Or the military base that their father was stationed at ... it's usually something very specific, and it's just too time-consuming to answer 100 percent of the requests."
Harford County Executive David Craig began collecting postcards about 10 years ago, after he saw the collections of friends. Since then, he has amassed a collection of hundreds of cards.
He even compiled a book of postcards, called Greetings from Havre de Grace, and is working on a book filled with Gettysburg postcards.
He said he relates to the older postcard collectors.
"Most of us collected baseball cards when we were boys, and our mothers threw them all away," Craig quipped. "Postcards give us something else to focus on."
He collects mostly Havre de Grace postcards, but he also favors postcards that depict Maryland racetracks, the Civil War, U.S. presidents and elections, he said.
Unlike most collectors, Craig isn't as interested in the main subject of the cards as he is in what's around it, he said.
"I may get a postcard that shows Havre de Grace High School," he said. "But I am more interested in the house in the postcard that no longer exists."
Joseph Carr collects hometown cards -- Salisbury, his hometown; Bel Air, his wife's hometown; and Delmar, his mother's hometown.
"The cards that mean the most to me are the ones that show places that have been a part of our lives," said Carr, 66, of Havre de Grace. "Sometimes there are cards that show buildings that we have never seen, or that no longer exist. Those are the ones that I want."
Martin said some customers are persistent. One collector contacts her five or six times a year trying to persuade her to part with her postcard of the Havre de Grace opera house.
"It's not an easy one to find, so I won't part with it," she said. "He tries to trade me for other things all the time, but I keep telling him no."
Martin, who has created 40 books on cities, states, geishas, logging and surfing, is collecting postcards that depict trailer parks from the early to mid-1900s, she said. Although the cards typically go for a few dollars, when dealers hear she is looking for a certain topic, the prices go up.
"When Mary Martin starts to collect, the prices go up," she said. "People think that if my company is buying them, then we must know something they don't. I try to keep it a secret what I am looking for, but everyone knows me, and they watch what I'm buying."
"Mary drives the prices like Martha Stewart did with china she showcased in a magazine," said Carr, a retired county school teacher.
Recently Martin purchased a trailer park card that should have cost $4. She paid $40.
Despite the elevated prices, Martin said she buys the cards she wants.
"There are no prices that are too high for me, if I want a card. Sometimes it feels like we spend more than we make, but we don't."
The show will be held at the Havre de Grace Community Center, at 1 Lagaret Lane. Hours for the show are 10 a.m. to 6 p.m. April 4, and 10 a.m. to 4 p.m. April 5. Admission is $3. Information: 800-899-9887.