(CBS News) NEW YORK - The midday rally in Lower Manhattan began with crowd chants of "I am Trayvon Martin." But the crowd of hundreds fell silent when Trayvon Martin's mother, Sabrina Fulton, spoke of her late son being killed by a single gunshot to the heart while he was walking home one night in Sanford, Florida, 17 months ago.
"It's very important that parents, godparents, aunts, uncles, cousins -- you speak up for these children. Trayvon was a child."
Martin's father, Tracy, appeared at a similar rally in Miami, while protesters turned out in dozens of cities -- Philadelphia, Atlanta, Chicago, Oakland -- and in front of the White House in Washington, D.C. The rallies came a week after the acquittal of George Zimmerman in Martin's death.
After President Obama reflected personally on the trial yesterday, saying in part, "Trayvon Martin could have been me 35 years ago," rally leader Rev. Al Sharpton echoed the President Saturday.
"Profiling may not be as bad as the back of the bus, but you don't know the humiliation of walking into department store and you are assumed to be a suspect rather than a customer," Sharpton said.
Demonstrator Andre Thomas, 25, said the president's personal reflections on the indignities he suffered as a young man were a "kick in the pants" to protest the double-standard when it comes to justice and race.
"If Trayvon Martin had a gun and stalked Zimmerman, he'd be in jail," Thomas said. "Trayvon Martin didn't get a chance to live. He didn't even get a chance to grow up when he was shot, and his killer walks the streets."
Civil rights leaders want states like Florida to reexamine their "stand your ground" style self-defense laws that led to George Zimmerman's exoneration in Martin's death.
"There should not be a law that means that if you think you're under threat you got the right to kill somebody. That law hurts blacks, whites, Latinos, Asians. This ain't just a black thing, this is a human thing," Sharpton said.
"Are we going to let any citizen with a nine millimeter gun profile our children?" Martin family attorney Benjamin Crump rhetorically asked the crowd, which responded with a resounding "No!"
Demonstrators are also pressing the Justice Department to pursue a federal civil rights case against the former neighborhood watch volunteer.
That's the aim of a MoveOn.org petition that has nearly 600-thousand signatures.
It is backed by music superstars Jay-Z and Beyoncé, who made an appearance at the New York rally. Neither spoke, but Beyoncé said in a written statement:
"We are still struggling with the issue of inequality and the lack of value for a black man's life. Trayvon Martin's most basic civil right, the right to live, was violated."
That's why Hylda Clarke said she wanted to be at the Lower Manhattan rally.
She said, "Trayvon died needlessly. He was an innocent child, and he could have been my grandchild."