The group is Anonymous for the Voiceless, and the event format is called a Cube of Truth — a structured street demonstration against animal agriculture that the organization runs in cities worldwide. The masks are deliberate: they're meant to make the messengers anonymous, keeping the focus on what's on the screens rather than on the people holding them. Stationed outside the cube, unmasked members approach anyone who lingers to talk.

The format reads as performance art from a distance, which may be part of why a Reddit thread about the gathering last weekend drew genuine confusion before someone from the group stepped in to explain. "These happen pretty regularly on weekends in Union Square," wrote a commenter who identified themselves as a participant. "Please feel free to talk to anyone there not wearing a mask and learn more."

The cubeoftruth.com site lists active chapters in dozens of cities; the San Francisco contingent has been showing up at Union Square on and off for several years, typically on weekend evenings when foot traffic from shoppers and tourists runs highest. The tableau — still figures, glowing screens, the occasional person in conversation at the perimeter — lasts an hour or two before the group folds up and disperses.

Anyone cutting through the square on a weekend evening who stops at the sight of the masks: the unmasked person who approaches is not asking for money. They want to talk about what's on the screen.