The Sonic CD Sound Test can actually be used to see many easter eggs in the game, including a black image with many of these sonics with text saying "Infinite fun, Sega Enterprises, Image by Majin". (It is noted that while majin is a supernatural being in japanese, ot really is just a different way of reading Masato Nishimura's given name, like readin "Sean" as "Seen" instead of "Shawn".)