Body-sized cardboard effigies of lynching victims were seen hanging by nooses on Saturday at the University of California, Berkeley, a school official said, amid nationwide protests over the killings of black men by police officers.University police responded to morning reports of two cardboard cut-outs in public campus areas before a midday demonstration and march assembled on the campus in the Oakland area, spokeswoman Claire Holmes said. A third figure was also hung before all were taken down."It has been unclear to us whether this was racially motivated or part of the protests across the country against police violence," Holmes said, adding the images were disturbing and the school would investigate. There were no suspects.Thousands marched in Washington, New York and Boston on Saturday in largely peaceful protests over the killings of black males by officers in Missouri, New York, Cleveland, and elsewhere.Decisions by grand juries to return no indictments against the officers involved in the deaths of Michael Brown in Missouri and Eric Garner in New York have put police treatment of minorities squarely in the national spotlight.Two of the effigies, a black woman and black man, could be seen in images on Twitter with "I can't breathe" written across them, referring Garner's words to police as they subdued him, and which have become a rallying cry in demonstrations nationwide. The woman bore the name of Laura Nelson, who was lynched in Oklahoma in 1911.Protests have erupted in the California university town and other West Coast cities including Oakland, Los Angeles, and Seattle. But Berkeley is a far cry from its status as a 1960s-era leftist hotbed. It burst into the national consciousness in 1964, when students took over administration buildings to protest a campus ban on political activity that became known as the Free Speech Movement.