If you’re wondering what the rainbow pentagon thing is that a lot of accounts use, it’s the Fediverse logo :fediverse:
It’s a public domain / CC0 design, its original designer shared a high quality copy at https://commons.wikimedia.org/wiki/File:Fediverse_logo_proposal.svg
It represents all the different server types that make up the Fediverse (https://fedi.tips/what-other-kinds-of-servers-are-on-the-fediverse/)
(Note: There can be no official logo on the Fediverse as there’s no central authority to make anything official. However, this logo is by far the most widely used one.)
