SIN - N.

Single (or System) Identification Number. An ID number unique to each citizen. Many street people (nomads, derelicts) are said to be "SINless", i.e. without a SIN. This makes them unknown (non-existent) to the system. It allows them to move about in society more freely than a recorded citizen, but also allows the enforcers of society (police and corp. security) to punish/abuse them without due process since, technically, they do not exist.