I decided to do a joja run and was making a new character when my finger hit the \ key instead of enter. To my surprise, a \ did not pop up on the name screen. In fact, when you type this in fact I typed the following: name: @>/\}{ farm: [] and best of all, for fav thing, I put this - each "letter" has an attached sound effect as you type it $*=< .... is this like "the" secret? probably not. Sort of hope it is and my clumsy fingers have finally stumbled on to something good.
Most likely Concerned Ape has made his own in-game font and is never going to need symbols like @ or # but might need controller button symbols if he ever wanted to create a tutorial. The other symbols all seem to represent various emotions, these were probably used to express character moods in early development before CA drew and animated the little speech bubbles. Not sure about the sound effects though. I don't think it's a secret or anything but it's really cool that you've found this.
Yes; each of these appear in game. I was wondering if putting them in any of the boxes might unlock things, like having your name be 13 hearts
