Philadelphia's rally was one of more than a hundred noon "Justice for Trayvon" vigils Saturday outside federal courthouses across the country. The demonstrations, organized by the Rev. Al Sharpton's National Action Network, were intended, in part, to pressure the federal government to pursue a civil rights case against Zimmerman.
In New York, hundreds - including Jay Z and Beyoncé, as well as Martin's mother, Sybrina Fulton - gathered in the heat.
Fulton told the crowd that she was determined to fight for the societal and legal changes needed to ensure that black youths are no longer viewed with suspicion because of their skin color. "I promise you I'm going to work for your children as well," she vowed.
At a morning appearance at Sharpton's headquarters in Harlem, Fulton implored people to understand that the tragedy involved more than Martin. "Today, it was my son. Tomorrow, it might be yours," she said.
In Philadelphia, speakers addressed a range of social issues, and one Hispanic activist broadened the message, describing how racial injustices affect many groups. Cheering in assent was a white woman there with her young son, who passionately chanted.
Protest signs reflected stances such as "Justice 4 all Trayvons"; "Kill the Stand Your Ground law"; and "Being black is not a crime, being followed and shot dead is a crime."
Bearing a sign declaring Trayvon Martin "could have been" her son, her brother, or another member of her family was Geraldine Henderson, 49, of Mount Airy.
"He's getting to an age where he will start being affected by racism," Henderson said of her 11-year-old son, Jaylen, huddled with her under an umbrella deployed against the sun. "I just want to prepare him and tell him to speak properly, respect yourself and others."
She echoed the words of President Obama, who in remarks to reporters at a White House briefing Friday described the distrust many black men in America experience, such as car doors being locked as they walk down the street.
"There are very few African American men in this country who haven't had the experience of being followed when they were shopping in a department store," Obama said. "That includes me."
"We go through it, too, the black women," Henderson said.
Jaylen said he has had the experience of walking down the street with his friends and watching a white woman grab her purse and move it to her other shoulder. "I feel uncomfortable," he said, "when a person feels scared of me."
Saturday's rally briefly became a march when participants made a loop up Seventh Street, headed east across Arch Street, then back along Sixth Street to Market. They chanted, "No justice, no peace."
His face covered in perspiration from the oppressive heat, Nelson Wiley, 68, stood in the middle of the crowd in a dark-blue hooded sweater, refusing to take off the hood. Holding up a bag of Skittles and a drink - Martin had been returning from a trip to a 7-Eleven with the candy and an iced tea when he was shot - Wiley said he felt it important to represent the slain teenager.
"I think this symbolizes Trayvon Martin. . . . I know he had this with him; that's all he had with him," Wiley said.
Michael Coard, an activist and criminal-defense lawyer in Philadelphia who describes himself as "the angriest black man in America," spoke briefly to the crowd about systemic issues of justice.
"The law should be respected if the law is just. But if the law is not just, it should be ignored," Coard said. Parents need to ensure that their children understand the law, he said, and people must call for a federal prosecution of Zimmerman.
Attorney General Eric H. Holder Jr. said last week that his department would investigate whether Zimmerman could be charged under federal civil rights laws. Such a case would require evidence that Zimmerman harbored racial animosity against Martin. Most legal experts say that would be a difficult charge to bring. Zimmerman's lawyers have said he was not driven by race but by a desire to protect his neighborhood.
Coard urged the Philadelphia protesters to fight "Stand Your Ground" and "Castle Doctrine" laws that expand self-defense protections.
"We have two sets of justice in this country," said Donald Williams, 57. ". . . The prosecution is used to putting us in jail, not defending us. When the United States does a better job being an advocate for us, rather than a prosecutor for us, that's how they change."
Contact Jonathan Lai at 856-779-3220, email@example.com, or on Twitter @elaijuh.
This article contains information from the Associated Press.