The initials FCDG of Apple's mobile phone serial number mean: F: Zhengzhou Foxconn, C: Shenzhen Foxconn, D: Chengdu Foxconn, G0: Shanghai Heshuo, G6: Shenzhen Foxconn's new production line. Generally speaking, the serial number is mainly used to check the warranty status of iOS devices, and can also be used to identify the authenticity of devices. If the serial number can't find any information, the device is probably not genuine.