It's called micro-stamping. The technique has been around long enough to prove itself which may be one of its problems. The gun industry knows it works. That's why they are challenging micro-stamping in court. In California, the technology has been law since early last year.
Basically, micro-stamping ensures that when someone fires a semiautomatic pistol, an identifying code gets physically stamped onto the cartridge casing. The result is ballistic evidence that could be a boon to law enforcement. A single cartridge found at a crime scene could easily reveal the weapon used.
Readily linking a cartridge casing to the gun that fired it why not? This doesn't restrict weapons ownership. It simply makes it easier to identify a gun's make, model and serial number. While making it harder to traffic in firearms. It increases the chances that a gun used in a crime can be traced to its owner.
Naturally, the gun industry doesn't like it. But the American Bar Association does and everyone else should. While not a panacea for gun crime, micro-stamping is a step in the right direction. In a town that spends 38% of its budget on law enforcement, this is a crime-solving technology that everyone should support.