Marching down the streets from Los Angeles to Berlin, people hold signs with messages like “There is no planet B,” each adorned with a symbol: two triangles inside a circle.

That circle represents the Earth, and the two triangles represent an hourglass, which “serves as a warning that time is rapidly running out for many species,” according to the extinction symbol’s website. The symbol was created in 2011 by a London street artist who goes by Goldfrog ESP and seems reluctant to give media interviews. But in a conversation with Ecohustler, he says he was inspired by the history of symbols. “I was making protest art about the declines of various individual species for awhile, but it felt quite inconsequential in relation to the scale of the problem,” he told Ecohustler. “I was thinking about how the environmental movement didn’t really have a well known [symbol] of its own.”