In a society defined by the haves and the have-nots, the sharpest line between them is the possession of a System Identification Number or SIN. A combination of citizenship, a passport, voting rights, and taxation obligations, it gives you the ability to live and work legally. To be SINless is to fall outside the system on almost every measure - no support, no right to employment or vote, unable to use public facilities or transit, turned away from shops and restaurants.
SINs are issued by a wide variety of governmental and extra-territorial corporate entities. They can be granted by birth or by a similar process to obtaining citizenship. Sometimes, corps grant them to particularly desirable hires. Often, corps use the threat of revoking someone’s SIN to keep their workers in line.
Physically, a SIN is merely a string of alphanumeric characters. The only human-readable part of it is a prefix code indicating the issuing entity - country or corp - who owns and controls the SIN. What counts isn’t so much the SIN itself as the data associated with it in various online hosts and datafiles.
SINs are the de facto unique identifier in the Sixth World. They are tracked everywhere, both in person and in the Matrix. Every interaction and transaction you have can be tied to your SIN and tracked in some database - and almost all of them will be. Hence every SIN has, trailing behind it, vast wakes of data, scattered across innumerable databases.
Those who don’t have a SIN - the SINless - are condemned to a life of misery. They are locked out of legal employment, of all banking, of reasonable healthcare. They cannot vote and they have no social safety net; even their basic civil rights are reduced. They face a lifetime of grinding for low cash-only wages and paying shady landlords high rent for shitty apartments, and praying that when they get sick there’s room at the charity hospital for them.
Matrix protocols have a special sidechannel for SIN broadcasts, beamed out at all times from your commlink. These broadcasts are not quite legally required, but in any lower-middle-class or better area, not having an active broadcast is a screaming red flag that will definitely attract attention. (Note that in very rough parts of town, the kind where police only travel in entire squads or not at all, broadcasting a SIN becomes a mark that you are easy prey. Choose wisely.)
SINs can’t separate the privileged from the scum unless there’s a way to know which is which.
Every SIN issuer makes available a listing of basic personal information associated with the holder of the SIN: name, date of birth, metahuman race and ethnicity, home address, stuff like that. If you attract the attention of a beat cop on the street, you can expect them to pull this up; and if your SIN is fake and the details don’t match you, well, you’re in trouble now.
Unfortunately for the police (but luckily for our plucky criminals), the SIN database infrastructure is run by for-profit corps, so carrying out a check like this costs a fraction of a nuyen. So penny-pinching corps like Lone Star and Knight Errant put their cops on quotas, preventing the authorities from just checking everyone they see.
If someone wants to go a bit further in verifying your SIN, the next step is to validate that the datastream attached to it looks legitimate. SINs are tracked everywhere, and that tracking information ends up in numerous databases owned by data brokers; these brokers' main line of business is selling access to the data to advertisers so they can track your every desire. But a lucrative sideline for them is running pseudo-AIs over each SIN’s profile to see how real it looks. This often catches out fake SINs, as generating a detailed, realistic, long-term history for a fake SIN is a lot of work.
This is the most secure form of check; gather one or more biometics from the person in question (finger print, retina scan, even a DNA swab) and compare them to the biometrics stored on file for the SIN.
Just one problem: jurisdictions. SIN issuers do not make these biometric files readily available to anyone who asks, because the corps do not trust anyone with that data. Outside of investigations of very serious crime (eg. terrorism), most of the time, the only entity that can check biometrics is the corp or nation-state that issued the SIN.
Every ‘runner has a fake SIN (or perhaps set of fake SINs) that they live their day-to-day lives under: buying groceries, paying rent, running their GridGuide subscription, that sort of thing. They don’t use this for criminal work, because it would make them far too easy to track down. There is no overhead associated with this, it’s absorbed in day-to-day living costs.
Although they last a long time, these fake SINs aren’t particularly good, and can’t pass a lot of inspection. Most people interacting with it – like ‘runner’s landlords – most likely know it’s fake, but aren’t the kind of people who are looking too closely. This is one reason ‘runners tend to live in the less gentrified neighbourhoods.
Where necessary, ‘runners can buy extra fake SINs for a job (1 LP for a SIN, 0.25 LP per type for a licence - civilian or security firearms, magic, cyberdecks, security-spec vehicles or gear. Milspec gear like APDS or Ex-Ex ammo, heavy weapons, very heavy armour cannot be licensed this way.)
A fake SIN will pass simple ID checks from a beat cop on the street automatically. The fake datastream associated with the SIN might stand up to a consistency check, should the ‘runner try anything that might provoke one; for example, infiltrating a secure area through the front door via a fake identity. In game terms: roll a Notice check for whoever is inspecting the SIN to see if they spot any weirdness in the analysis results. This might be a +/- 1, depending on the resources of the corp doing the check.
Gear licences for these SINs are “open carry”, in the sense that the presence of the licence is automatically broadcast alongside the SIN. This can (obviously) attract attention, and often does.
Fake SINs are inserted into tracking databases via hacks that are quickly discovered and deleted. They are typically only useful for a week or so.
If you’re really up to something nefarious, you can purchase a high-end fake SIN - 4 LP for the SIN, 1 LP per licence.
These are far better quality, with skilled counterfeiters creating near-impeccable fake histories spanning multiple databases. They pass all simple ID checks and consistency checks automatically. They might, or might not, pass a biometric test run against the SIN database of whoever ostensibly issued the fake. In game terms, this is a Notice check by the host/system running the scan - typically a d6-d10 rating.
Licences on high quality fake SINs can be open carry, or if the purchaser prefers, “concealed carry” – meaning the SIN broadcast does not tag the person as carrying concealed weaponry. They are still licensed, however, and get to be extra rude and snooty to any beat cops who notice their gun, stop them assuming they are unlicensed, then discover they are (seemingly) VIPs.
High quality fake SINs are still deleted after ~1 week, though, just like low-quality ones.
Although many SIN issuers do gather and store a biometric profile, they don’t make this information available to the authorities (except, rarely, in the case of high-profile crimes like terrorism.)