I don't know if this should be a guide, but I couldn't find a better place to upload this information.

So whenever I try and see if anyone knows what Hat Kid's signature is I only see people wondering if it is her real name in another language. I never seen anyone find what her signature actually is.

You don't need to decipher the signature to find out what it is. It actually shows up in a different part of the game. If you play the Rumbi Factory and get one story book, you can see it. The first page shows Hat Kid through Rumbi's eyes.










If you look at the bottom left of the picture you can see Rumbi's ID.








And these are the same symbols as Hat Kid's signature.










So Hat Kid's signature is her Rumbi's ID. She would know what the ID looks like because it looks like Hat Kid had to build, or fix her Rumbi.

That is all I got. Sorry if someone else made something like this before, but I couldn't find any posts that said this.