Every piece that leaves carries a serial: IPO, a number, MNL. It's engraved small, usually somewhere only the owner will find it.
We do it because a made thing deserves a record. The number says this one was logged: what it's made of, when, and who it was for. That's the line between something off a shelf and something that was, for an afternoon, the only thing on the bench.
It's also a quiet promise. Come back in five years with a worn edge and the number tells us what it was and how it was made, so we can put it right. The serial isn't branding. It's memory.