A police officer (L) looks on as Greenpeace activists hang a banner at the Estela de Luz (Pillar Of Light) monument during a protest against genetically modified seeds which they say threaten Mexican corn, in Mexico City May 16, 2013. Four Greenpeace activists climbed the monument to demand that Mexican President Enrique Pena Nieto's government reject the commercialisation of genetically engineered (GE) corn seeds in Mexico. Genetically engineered corn does not exist in Mexico yet, but Greenpeace says, multinational firms have requested permission to plant their seeds in the country. The letters on the monument are part of a message that reads, "No OGM" (Genetically Modified Organism). REUTERS/Henry Romero (MEXICO - Tags: FOOD CIVIL UNREST SOCIETY ENVIRONMENT)