The officer later apologized, but a global movement, nourished by posts on Facebook and Twitter, was born.
The first SlutWalkers stepped off in Toronto in early April. Since then, marchers have taken up the cause in Seattle, Boston, Chicago, and other cities, as well as in Argentina, England, Australia, and Sweden.
Much of the media coverage has focused on the alluring outfits some SlutWalkers wear, but many participants dress more demurely. At the Toronto SlutWalk, one woman carried a sign that read, "I was 14 and raped in a stairwell wearing snowshoes and layers. Did I deserve it, too?"
Many who have participated are young women, but mothers have also marched with their adult daughters in some cities.
Philadelphia's SlutWalk begins at 11 a.m. Saturday at 11th and Pine Streets. Marchers will head from there to City Hall.
Speakers at the event will include Qui Alexander, a transgender man and an educator at Philadelphia's Mazzoni Center, which provides health-care and other services to lesbian, gay, bisexual, and transgender people; Stephanie Gilmore, an assistant professor of women's and gender studies at Dickinson College; Deepa Kumar, associate professor of media studies and Middle East studies at Rutgers University; State Sen. Daylin Leach (D., Montgomery); and Aishah Shahidah Simmons, a survivor of rape and incest who made the movie NO! The Rape Documentary.
Altman, who lives in West Philadelphia and is studying sociology and women's studies at Cornell College in Iowa, already had been working to raise awareness about sexual assault on campus when she heard about SlutWalk.
She has turned the local walk into a summer project, helping negotiate for required city permits, organize, and raise money for the event.
She is not sure how many people will participate in Saturday's SlutWalk, but more than 2,000 people have "liked" the group's Facebook page.
Despite its origins in a police officer's comment, the SlutWalk name and concept have generated controversy and backlash.
Writing in the New York Times recently, Rebecca Traister lamented: "I wanted to love SlutWalks. . . . But . . . I have mostly felt irritation that stripping down to skivvies and calling ourselves sluts is passing for keen retort."
Altman, who had not seen Traister's essay, said the name aimed to make a point, too.
"Slut is a word for a woman who has sex, sometimes with more than one person," Altman said. "Why is it OK for a man to do that and be considered a stud, but a woman is called a slut?"
David Buss, a professor at the University of Texas and author of Evolution of Desire and other books about human relationships, said he and other researchers found that women are more likely than men to call women "sluts" and other derogatory names. There are also about 35 words used to describe women who have many sexual partners, and most of them are negative, compared to only a few for men.
Researchers also have found that only a "a small subset of men commit the majority of rapes," Buss said. "These are men who are high in psychopathy, low in empathy, high in short-term mating strategies."
Men who commit sexual assault also often have derogatory attitudes toward women, Buss said.
Simmons, the documentary-maker who will speak at the event, said SlutWalks also raised complicated questions about women and clothing. Even in countries where women are legally required to cover their entire bodies, sexual assault occurs, she said.
Marching in provocative dress may be a "made you look" way to get people talking about sexual assault, but it has worked.
"We do have to talk about these complexities and what does it mean to march in a thong," Simmons said.
Philadelphia SlutWalk organizers estimate that they need $4,000 to $10,000 to cover the costs of their demonstration, including paying for a stage, sound, T-shirts, and water. They will hold a fund-raiser from 7 to 10 p.m. Monday at the Fire, 412 W. Girard Ave. There is a $10 cover, and several artists will perform.
Contact staff writer Miriam Hill at 215-854-5520, firstname.lastname@example.org, or @miriamhill on Twitter.