SIN (System Identification Number), is one’s ID and much more. It is the key ta a database containing any official information regarding a person, so it also functions as one’s bank account, passport, driving – or any kind of – licence. It also contains one’s criminal record, and their transaction history and employment information can be traced through it. A valid SIN is also necessary to be authorised to have a Matrix connection. The SIN is stored in a SIN chip, which is usually situated within one’s comlink.
After the crash of 2064, SIN usage is regulated by the Global SIN Registry, which operates under the aegis of the Corporate Court. Sovereign nations and corporations of AA status or above, are allowed to grant SIN numbers to their legitimate citizens, but obliged to share their database with the GSINR.
Flashing one’s SIN is necessary for most operations nowadays, like using public transport, making any kind of transaction, proving one’s identity etc.