In most places it was too hot for hooded sweatshirts.

So they came with T-shirts. In Washington, Elaine Morris showed up in one bearing a picture of slain teen Trayvon Martin alongside members of the Ku Klux Klan, with the slogan “Which hoodie looks suspicious?” In Chicago, CeCe Fannin handed out white T-shirts emblazoned with the words “I mean no harm” — for black youth to wear, she said, to make clear they are not a threat.

In cities around the country, demonstrators gathered in support of the unarmed black teen in the now-iconic hooded sweatshirt whose shooting death in Florida last year inflamed racial tensions and raised questions about whether young black men are viewed more suspiciously than their peers of other races or ethnicity.

The purpose of the rallies, organizers said, was to press for a federal civil rights prosecution in the case and to call for changes to state gun laws.

But for many of the protesters and speakers, they provided an opportunity to express their outrage that George Zimmerman, the neighborhood watch volunteer who shot and killed Martin after a confrontation in February 2012, was found not guilty of a crime by a jury on July 13.

“I support the rule of law,” Lennox Abrigo, D.C. chapter president of the National Action Network, an advocacy group founded by the Rev. Al Sharpton, told several hundred protesters outside the federal courthouse in Washington. “But I disagree with every cell of my body with that verdict.”

John Allen, 23, was among several thousand demonstrators who gathered outside the federal building in downtown Chicago.

“It makes the United States look crazy,” said Allen, who lives on the city’s south side. “Here we are talking about freedom, and we let murderers off after killing a child.”

The case sparked outrage in part because a 911 recording appeared to show that Zimmerman provoked a confrontation with the 17-year-old when Martin was walking through the Sanford, Fla., neighborhood. Zimmerman was concerned about a string of burglaries in the community. Critics of the decision believe he was suspicious of Martin because of Martin’s race and clothing.

Defense attorneys argued that the two got into an altercation in which Martin had the upper hand and Zimmerman, 29, feared for his life. Zimmerman’s supporters have argued that race did not play a role in the shooting. Zimmerman has a white father and a Peruvian mother.

According to a recent Washington Post-ABC News poll, eight in 10 blacks say they think Martin’s killing was not justified, compared with 38 percent of whites. Most whites say they do not know enough about the shooting to determine whether it was justified.

Many at the rallies called for action to repeal or change “stand your ground” laws. Thirty states have adopted a version of the law, which removes a once widespread requirement that a person claiming to have killed someone in self-defense must have had to try to flee the situation first.

During Saturday’s protests, many took up the term “stand your ground” to represent their own response to the Zimmerman verdict.

“I pray we’ll stand our ground against unemployment, failed education, poverty and the other evils that have created an atmosphere of violence and hopelessness,” said the Rev. Michael Pfleger, a prominent Chicago priest and anti-gun crusader.

On Friday, President Obama addressed the anger over the Zimmerman verdict, urging critics to protest peacefully. He spoke in deeply personal terms about times when people viewed him with suspicion because of his race. And he urged scrutiny of stand your ground laws.

There were no reports of violence Saturday as demonstrations were to take place in more than 100 cities, including some where the temperature topped 90 degrees. Thousands reportedly showed up to a rally in Miami. Many of the demonstrators were African American and carried signs that said “Black life matters” and “I am Trayvon Martin.”

In New York, Martin’s mother, Sybrina Fulton, wore a shirt bearing her son’s face framed by a green hoodie. She pledged to keep up her activism on her son’s behalf despite the verdict of not guilty.“We have moved on from the verdict,” she told the crowd. “Of course we’re hurting. Of course we’re shocked and disappointed. And that just means we have to roll up our sleeves and continue to fight.”

In Oakland, Calif., the weather was more temperate than elsewhere in the country, leading 13-year-old Sherekhan Adams to show up to the rally in a gray hooded sweatshirt and a sign that read, “I fit the profile. Am I next?”

The gathering of about 400 people in front of the federal building there began on a fiery note, urging social change. But over the course of the event, the speakers turned inward. “We have to remember that we have to carry ourselves in a certain way. . . . We have to carry ourselves like we value our lives,” 16-year-old Cai Johnson told the crowd.

But in some corners of the country, the anger was still palpable. Cynthia Savage, 55, a quality assurance consultant from Clinton who attended the District rally wearing a “March for Justice for Trayvon Martin” T-shirt, said she was not surprised by the verdict because she believes that racism is still prevalent in the United States — and that it extends to the courts.

“How can you trust the jury system when it’s already biased?” she asked.

Lydersen reported from Chicago. Gregory Thomas in Oakland and Sean Sullivan in Washington contributed to this report.