For example, I have seen someone with the music note symbol, and I'm confused on how to get these, because I want them.
2Please don't just create new tags. There's no real reason to create a new tag that's specific to mii creation.– FrankApr 18, 2016 at 22:04
Open the Mii Creation.
Under "User Settings" choose "View/Modify user information", skip the body editing and you can change your nickname.
Now, if you press the small keyboard icon (near "z") on the keaboard on screen you can access every special keyboards and characters.
What you're looking for is under SYMBOL:
In the third page you can find the musical note character ♪.