Hyokkori Hyoutanjima: Hyoutanjima no Daikoukai/Hidden content
From Sega Retro
Sega logo ™ symbol
While not released outside of Japan, code exists to add the ™ symbol to the introductory Sega logo if the game detects it is being played on a Western system.
Level select
On the title screen, press 
START . A number will appear above the title. Press / to toggle the number, and START to start from the selected level.