My daughter met the old man while Christmas caroling, and he gave her what seemed to be a puzzling gift: a hand-drawn cartoon of a bald man peeking over a wall with the inscription, “Kilroy Was Here.”

He was an Alzheimer’s disease patient, so Veronica assumed that the note didn’t mean much, just a kind and fanciful offering.

“Was he a World War II veteran?” her Dad and I asked, knowing full well the answer.

We explained that “Kilroy Was Here” was the mischievous calling card of countless American GIs in the ’40s when they were stationed overseas.

It was, of course, something more than that — at once a stamp of individual identity and a show of support for fellow GIs around the world. “Kilroy was here was just ubiquitous,” said Jeff Underwood, historian for the National Museum of the U.S. Air Force. “Wherever Americans went, that graffiti went with them.”

It was forbidden, but that didn’t stop the GIs from leaving their mark whether they were storming beach-heads, destroying underwater obstacles, moving tank columns into Italy or even imprisoned in POW camps. “It was a nice irreverent way of telling the other guys, ‘Ha ha, I was here before you; I won the race,’” Underwood noted. “It was also a way of saying there was someone there with you, that you’re not alone.’”

The origins of the phrase are a bit mysterious, Underwood said, but it probably started with a Massachusetts shipyard inspector named James Kilroy who initialed “Kilroy was here” as the ships were being built. “The GIs saw that and it stuck,” Underwood said.

Underwood isn’t surprised that veterans might remember the slogan at a time in their lives when they might have trouble calling up the names of their grandchildren. Patients with any sort of dementia still can provide invaluable oral histories, he said, “because their wartime experience is such a vivid experience for them.”

Lauren Kerr, associate director of programs for the Miami Valley chapter of the Alzheimer’s Association, said: “I have heard it referred to as the unzipping of memory. As the short-term memory becomes worse, the long-term memories seem to be what lasts, especially when there is emotion associated with the memory.”

Many of us have experienced the same phenomenon in our own families. I had an uncle who never mentioned a word, in his final years, about his brilliant 50-year career. But I didn’t doubt the accuracy of his vivid memories of more than 30 missions as a B-17 pilot.

Kilroy was here. What was once an inescapable part of our popular culture seemed like hieroglyphics to my daughter, even though her grandfather is a World War II veteran. It speaks of the power of the generations sharing their stories with one another. Underwood urges families to conduct oral histories with their veterans, using the instructions provided Veterans History Project of the American Folklife Center at the Library of Congress (http://www.loc.gov/vets/). “It becomes part of the family story, and it does tie the generations together,” Underwood said.

When I was growing up, most of the Dads, my own included, were World War II veterans. No big deal. My Dad’s father was a World War I vet — again, nothing noteworthy for his generation.

Yet what had once been as common and as overlooked as dandelions had become, with little notice, the most precious currency of all. Eight years ago, I interviewed a half-dozen World War I veterans among the 1,000 then still living in Ohio. Today there are no known survivors among the tens of millions who served worldwide. Florence Green, a member of Britain’s Royal Air Force who died in February at 110, is believed to have been the last living veteran of the war to end all wars.

These veterans never thought of themselves as a big deal, either. It is only now, in this late hour, that we are beginning to realize our indebtedness to our World War II veterans.

I think that’s why I was so moved by the scrawled note from my daughter’s new friend. Even as he was losing his memory, this veteran showed the playfulness, individuality and sense of solidarity symbolized by the American GI’s most famous catch phrase. Even as he was battling Alzheimer’s, he hadn’t lost his core identity. It’s as if he was saying, “I mattered. And what we did mattered.”

How lucky we are that Kilroy was here.