Father of teenager killed in school shooting designs billboard with bracing message: “Vote for Me.”

A Stop Handgun Violence billboard went up at the garage at 50 Dalton St. Tuesday.DAVID L. RYAN/GLOBE STAFF

A few years ago, Joaquin Oliver asked his father what he wanted to be when he grew up.

It was a joke, of course. Manuel Oliver was already grown, living in Parkland, Fla., watching Joaquin make his way through high school. But he played along, telling his son he wanted to retire, ride his motorcycle, maybe spend time with grandchildren one day.

Then he asked his son the same question, Manuel Oliver recalled Monday.

“I wanna be great,” Joaquin told him. “I wanna be known everywhere. I wanna be like [Nelson] Mandela, or John Lennon.”

Two years ago, Joaquin Oliver was among 17 people killed in a school shooting in Parkland. He would have turned 20 last week, and this fall could have cast his first vote in a presidential election.

His image is now being featured on a new billboard, designed by his father, that urges people to vote in bracing words.

“I was murdered. I can’t vote. Vote for me!” reads the billboard, posted on a parking garage in the Back Bay that is visible from Boylston Street.

The message is delivered in the first person to carry Joaquin’s voice, his father said.

“I know him so well,” Manuel Oliver said of his son. “We not only had a relationship like son and father, but also like best friends. I know exactly what he would be doing at this point and what would be concerning him.”

The picture of Joaquin, who was affectionately known as “Guac,” is printed in high-contrast black and white next to his name and date of death, Feb. 14, 2018. The message “Vote for me!” has a dual meaning, Manuel Oliver said. It urges people to vote on behalf of Joaquin and the thousands of Americans killed by guns every year, and to vote for people like Joaquin to represent his memory in the halls of power.

Manuel Oliver, an artist and designer who still lives in Parkland, turned to activism around gun laws after his son’s death. He and his wife, Patricia Oliver, founded a youth leadership group called Change the Ref — short for referee. They met John Rosenthal, cofounder of Massachusetts-based Stop Handgun Violence, at the “50 Miles More” march from Worcester to Springfield about six months after their son’s death.

This is their second collaboration with Stop Handgun Violence, the organization known for eye-catching billboards advocating for gun safety. The new billboard is also set to be posted this week in New York’s Times Square, Miami, Atlanta, and Las Vegas.

While public attention has been focused on the coronavirus pandemic and protests about police brutality and systemic mistreatment of Black people, laws that regulate firearm sales and access should still be on voters’ minds as they choose their candidates this fall, Rosenthal said.

“It’s so critical that we honor our democracy that we are rapidly losing to special interests and vote,” Rosenthal said. “Americans should ask candidates at every level what they’ll do about gun violence and what specific actions they’ll support, starting with criminal background checks on all gun sales and renewing the ban on military-style weapons.”

Joaquin Oliver also appeared on the group’s last 90-by-20-foot billboard at the same location, also designed by his father. It carried the words, “If I had attended high school in Massachusetts instead of Parkland, Florida, I would likely be alive today.”

“Only a mom or dad could put those words in their son’s mouth,” Rosenthal said.

Rosenthal and Stop Handgun Violence were long known for posting massive billboards by the Massachusetts Turnpike near Fenway Park. The billboards, which advocated for various laws the organization backed or featured a tally of the number of children lost to gun violence, hung from the Lansdowne Street parking garage Rosenthal owned.

Rosenthal sold the garage to the Red Sox’s parent organization in 2013 and removed the turnpike billboard two years later.

The organization has since replaced that billboard with smaller, usually donated calls for action along highways and city streets.