Pick up a LEGO box and the minifigures are hard to miss. On kids' sets they're all over the front, right in the thick of the scene, and often lined up again on top in action poses. Adult sets play it cooler: the cast stands in a calm row along the top or side of the box, like actors taking a curtain call.

Somewhere between finding the right set and actually paying for it, a strange word ambushes you: Icons. Or Technic. Or Friends, which is not the sitcom. These are LEGO themes – the company's way of sorting a few thousand products into families – and nobody bothers to explain them to newcomers.

Display-ready LEGO sets give themselves away on the packaging – you just need to know which details to check.

The piece count is a decent clock, a mediocre difficulty rating, and a genuinely terrible tape measure.

18+ LEGO sets are the ones the LEGO Group designs for grown-ups first – and the black box is how you spot them from across the aisle. Here's what the label really promises, what it doesn't, and why it takes most of the risk out of giving an adult a box of bricks.