I just saw a cashier with the world’s smallest stud-like “earring” in her nose, and I don’t get it. It is sooooo small, does it have a backing? Or, is it just stabbed into her skin like a tie tack (without a back)?
It’s probably one like this. I’ve seen these called pins, studs, fishtails, and screws… some places sell these straightened out so that you can bend the pin to your own preference. The bent pin holds the pierce in, and avoids the irritation a stud back would cause inside a nose. A lot of people use these styles for labrets as well-- the tail is bent to fit comfortably between lip and gum. It could also be a flat back barbell.
(I’ve also seen a number of people wear plain studs sans back as you describe it-- especially those who’ve pierced their noses themselves by simply jabbing a spare ear stud through their nostril. These are the types of people who then complain that their nose pierce never heals properly.)
It is also possible to have near-invisible jewelry to satisfy regulations. I know people who insert monofilament fishing line through a piercing, then heat the exposed end, which melts into a small blob.