When a boy grows up he starts to pull his hair to the top and tie it into a topknot called a sangtu.
Usually, it’s held together by a pin called donggot which is basically a binyeo that is together with a manggeon (headband) and gwanja (little gemstones) used by men to keep the hair from falling out of the knot.
LS often wears a little golden crown known as sangtugwan to cover his topknot that is specifically used by kings and crown princes. The coronet seems to consist of two parts – the actual crown and the pin that fastens it to his hair.
However, it’s traditionally composed of three parts – a te which surrounds the topknot, a dari which is attached to the front inside and the back inside of the te and finally a jamdo that fastens the cap to the head.
So far, we have seen him with three types of sangtugwan and I couldn’t help myself but to squeal in glee when I saw him wearing the one with the heart-shaped pin wearing during the bed scene.
Sources: wikipedia.com, , http://www.bonamuseum.com,