Secret Message from Miyamoto
When in Samus' ship, go to the radio and press the following symbols:
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Going from left to right, press the eighth symbol, the third symbol, the fifth symbol and then the fourth symbol.
You will then hear a message from Mr. Miyamoto!
A rough translation:
Ah, can you hear me? This is Miyamoto.
All of you playing Metroid, can you hear me?
Its fun, isnt it?
Ive also worked on many [Metroid] games, but this one is the best yet, dont you think?
Definitely play it all the way to the end.