Alnylam staff member Chris Theile works on signs for this weekend’s March for Science.

The March for Science, happening Saturday in more than 600 cities across the world, is an explicitly political movement. But it's trying hard to be seen as nonpartisan.

"The goal of the march itself is to highlight the valuable public service role science plays in society and policy and demonstrate the deep public support for science," the organizers say on the March's website. "We take strong stands on policy issues based on the best available scientific evidence, but we will not let our movement be defined by any one politician or party."