In the 6th World, a SIN is a System Identification Number.
In Corporate SINs Edit
This is the meaning of SIN in Corporate SINs, though an obvious pun may have been intended as well.
In the Corporate MetagameEdit
Seattle Street News gave this definition of a SIN:
SIN… the System Identification Number. It was brought into being first in the UCAS in 2036, and everyone else adopted the idea. Nations gave SINs to their citizens. Megacorps, who have become nations themselves, gave SINs to their own citizens. The SIN is assigned to each person in society and you need to have one to be accepted in security systems and government databases and pretty much any computer anywhere that authenticates people’s identities. A SIN identifies a person in the global information system and is attached to every piece of information generated about you, from where you go on the Matrix, if you have cavities, what brand of cigarettes you smoke, what sort of health insurance you have—and note, your health insurance is going to see that you smoke and hold it against you. Your SIN must always be legally be broadcast. So when you are walking down the street, your SINner status is always on display for Law Enforcement or Advertisers to see. It may seem Orwellian, but it puts you in society. If you don’t have a SIN, you are a not a person in society. You are on the edges and in the shadows. You can’t get a job. You can’t buy food. Without your SIN beamed to all, you can’t get into fancy museums. You might be picked up by Law Enforcement for just walking down the street. Some corp types don’t even see you as a person. You do not exist. You are not seen.