How does iphone5s add default signature at the end of SMS?

Setting the SMS signature is simple: click Settings-General-Keyboard-Add a new phrase-(your name), and then click Enter Code-enter two letters that you can easily remember. -Last point: storage. It's over. For example, I want to send my phrase (unit: XXXX, name: XXXX, email address: XXXX) to the other party. My input code is KK. After writing the theme, you can start a new line. Type KK, and then click the space to build it.