For three hours under a searing sun, people walked up to a table on the District’s Freedom Plaza on Sunday and signed notecards that would be sent to military members and their families.

“Thank you for your service,” was the quick message from most, sometimes in block letters, sometimes in the curlicues of tweens, sometimes with an exclamation mark to drive home the gratitude.

And then Cherry Kwunyeun took up a black pen.

“Having survived 9-11,” she wrote, “I appreciate your dedication and sacrifice for making a more loving and safer community globally.”

A decade after the Sept. 11 attacks, remembrances both grand and intimate in the Washington area marked the day. Included were moments somber and reflective but also optimistic and forward-looking.

Kwunyeun, 34, of Catonsville, Md., said she usually returned to New York to mark the anniversary — back to the city where she had been working at the World Financial Center on the morning of the attacks. She watched the second airliner hit the twin towers as she fled.

She said she that saw police, firefighters and “military uniforms helping us” and that “it changed me.”

On track for a career in global investing, she said, “I started thinking about those men and women who were sort of invisible to me,” and later “why did this all happen to America?”

Kwunyeun stepped off the track, won a Fulbright scholarship for international study in micro-finance and now develops business models that link local artisans and small entrepreneurs from various countries.

This year, she opted to stay in Washington for the volunteer sign-up on the plaza on Pennsylvania Avenue organized by HandsOn Greater DC Cares as part of the national 9/11 Day of Service. About 1,200 people registered for projects that will stretch through the year. On Sunday, they included making math puzzles for students, assembling seed packets for community gardens and sending the notes through the Blue Star Families support network.

The signers also pledged to volunteer for a public-service project of their choice. Kwunyeun, a Thai American, pledged 50 hours working with Thai youth on educational activities.

That common thread of recognizing service to others wove through commemorations.

In Prince George’s County, about 80 firefighters in full gear did laps up the stairs of the Maryland Trade Center in Greenbelt to honor the ascent of the New York firefighters who hustled into the burning towers. Each carried a photo of a firefighter who perished.

The climb, and others across the country, raised money for the National Fallen Firefighters Foundation.

In Purcellville, the town unveiled its monument to emergency workers: Its base is a stone from a barn in Shanksville, Pa., the top is a 3-by-1-foot portion of an I-beam from the twin towers, and the flag overhead was flown at the Pentagon.

The nod to the three sites of the attacks, said Mayor Bob Lazaro, touched “the deep feeling of love in their country.”

In Baltimore’s Inner Harbor, rain glistened on the slab of white marble holding up three massive steel beams from the North Tower — a memorial to the 68 Marylanders who died.

“They are twisted, torn and tattered unlike any steel you have ever seen,” said Randall M. Griffin, chairman of the memorial committee.

Away from formal speeches, D’Juan Thomas of Alexandria paused for a quieter gesture. At 22, he is a graduate student in counseling at George Washington University and volunteers through his church to work with young people.

Picking up a pen as Kwunyeun had done, Thomas wrote the standard “I want to thank you for your service” on his card, paused and added: “It may seem that we have forgotten about you but we haven’t.”

Staff writer Sylvia Carignan contributed to this report.