Is the katakana of Kudou Shinichi: ツソィチ? クドウ

Because this letter was written to him by Xinyi's father; At the end of the letter, Shinichi. K is the name of Kudou Shinichi written in Roman characters;

And the writing of this K is the consistent usage of Kudou Yū saku; So Conan knew that this was written to him by his father more than ten years ago; The subtitle at the end just wrote Kudou Shinichi's katakana to tell the audience that Conan already knew. ...

I hope I can help you! Please accept it if you are satisfied ~ Please ask questions if you have any questions ~