Because of the security of the third edition of Saipan system, most software on the system needs certificates to make the software run on the corresponding machines. Each mobile phone has its own unique serial number (IMEI), and the serial number has a corresponding certificate. The certificate contains the serial number information of your mobile phone and some permission settings. The signature is to brand the software you want to install with your mobile phone (especially SISI, SIXX extension). With this brand, your mobile phone can correctly identify the software you installed. Some mobile phone software must be signed before installation, of course, there are also software that does not need to be signed. These are generally released by enterprises, so you can use them with confidence.