If you've ever wondered what 
means, it's the logo of the Fediverse!
There is no central authority to decide an official logo, but is by far the most commonly used logo and most widely accepted.
The designer of the logo uploaded high quality versions of it to Wikimedia Commons:
➡️ https://commons.wikimedia.org/wiki/File:Fediverse_logo_proposal.svg (colour)
➡️ https://commons.wikimedia.org/wiki/File:Fediverse_logo_proposal_(mono_version).svg (monochrome)
Fediverse projects often use this as the basis for their own logos by tweaking it a bit.