In fact, signature is the threshold of software. In order to prevent some malicious software, the software in sis (or SIXX) format of Nokia smartphones needs to be signed when it is installed. Because signature costs money, some small software needs to apply without its own signature. You can apply for signature free of charge on websites such as Saipan Smart Phone Network, Ouku Network, or Mobile House, and then sign the software according to the instructions. The signed software can be officially installed and used when it is put into the mobile phone.

There is also a tutorial on cracking and understanding mobile phones online. After the phone breaks down, you can install the software without signing. Baidu has many tutorials at once.