Iron Man/X-O Manowar in Heavy Metal (Game Gear)/Hidden content
From Sega Retro
Sega logo ™ symbol
While not released in Japan, code exists to remove the ™ symbol from the introductory Sega logo if the game detects it is being played on a Japanese system.
Select mission
Enter PKTPCN as a password. When the game begins, pause, then unpause while holding or .