An activist threw ink on an image of Chinese President Xi Jinping. Now she's disappeared.

A young Chinese activist named Dong Yaoqiong filmed herself throwing ink on a poster of Chinese President Xi Jinping, who in March obtained legal authority to stay in office indefinitely, and posted the video online. "I oppose Xi Jinping and his authoritarian dictatorship," she said. "Let's see how he's gonna deal with me." In a later post on Twitter, Dong shared a photo that appeared to show police waiting outside her apartment. "Right now there are a group of people wearing uniforms outside my...