The Marvel Cinematic Universe really set a precedent for post-credit scenes. They obviously existed before those films, but the MCU had people expecting movies to give you something special after the credits. Now people sit and wait after every movie to see if there's something special at the end.
We're happy to tell you that there is indeed something to wait for after Sonic the Hedgehog's credits roll. Now you can sit back and relax, let them scroll by, and get treated to a surprise. We're not going to tell you what it is...because we don't know! It'll be a surprise for all of us!