Some graduating Stanford University students carried signs at their commencement on Sunday, decrying a 6-month jail sentence handed to a former student convicted of sexual assault on the California campus, but protests did not disrupt the ceremony.

University President John Hennessy asked the crowd to join him in a moment of silence for the survivors of sexual assault and violence.

"Rape is rape" and "it doesn't matter whether she was drinking" read the signs carried by a handful of graduates as they marched in the traditional "Wacky Walk" processional at the Stanford Stadium.

And a plane commissioned by UltraViolet, a women's rights group, buzzed overhead trailing a banner that said "Protest survivors. Not rapists. #PerskyMustGo."

The tag refers to Santa Clara Superior Court Judge Aaron Persky, who handed down what many consider to be a light sentence against former Stanford student-athlete Brock Turner, 20, for his conviction in a 2015 sexual assault.

Turner's sentencing on June 2 gained international attention after a detailed letter that the victim had read aloud in court was posted online. It describes the devastation the woman felt in being sexual assaulted while unconscious after partying.

A Stanford law professor is leading a signature-gathering drive to remove the judge from office for handing down the six-month sentence even though prosecutors had recommended six years.

Jonathan Fisk, a 22-year-old earth systems program graduate from Long Beach, California, protesting on behalf of sexual assault survivors, said the tone around campus over the past week has been "less than celebratory."

The protesters' intention, Fisk said, was not to detract from the celebration, but to bring light to broader issues.

Not all were in favor of using the ceremony for political protest. Graduating senior Allie Koscove said the event was not the right platform: "The topic this morning at breakfast was the Brock Turner rape case and not graduation."

Speakers at the ceremony brought up the case.

"Violence in all forms has become a scourge on our society," Hennessy said in his final welcome speech as university president, before asking for the moment of silence.

Commencement speaker and Emmy Award-winning documentarian Ken Burns also acknowledged the controversy, noting that he is a father of four daughters. "If someone tells you they have been sexually assaulted, effing listen," Burns said to enthusiastic applause.

Persky is legally unable to comment on the case because Turner is appealing his conviction, Santa Clara County court spokesman Joseph Macaluso has said.