This Kransen is worn by Astrid Hofferson on her head throughout the entire franchise.
A Viking Kransen; Nordic definition roughly meaning "head wreath"; was a real accessory worn by unmarried girls during special occasions. Traditionally it was passed down from mother to daughter so a single kransen could last for many generations. Before her wedding ceremony, a girl would have it ceremoniously removed by her female attendants and replaced by a "wedding crown" to symbolize the end of her maidenhood. It would then be carefully preserved so it could be passed down to her daughter when she had one.
In the How to Train Your Dragon Franchise, Astrid wears hers every day, and appears to be wearing a new one in each film. She is the only Viking maiden ever seen wearing one. And so far it has never been physically or verbally referenced aside from being a part of Astrid's permanent character model.
The first film and TV series
Astrid is seen wearing the same kransen from her first introduction to the end of the TV series. It is worn over her hair in the back, and under her long bangs across her forehead in the front. By age 18, she's added a small braid over it on the left side.
The Kransen is also replicated in the live theater production of the first movie - the How to Train Your Dragon Live Spectacular. It is a metallic leather band with button-like metal circles around it.
Sometime between the last events of the TV series and the second film, she starts wearing a new kransen. Her hairstyle has changed slightly but she wears the kransen in the same manner as she had since the beginning.
From what we've seen so far, Astrid may have changed her kransen again, or possibly added decorations to the one she was wearing in the second film.
In the first film and TV series, Astrid's kransen is a brown leather band with two sizes of metal studs embedded into it for decoration.
In the second film, she wears a slightly slimmer leather band that is void of any decoration.
In the third film, she appears to be wearing a similar leather band with embossed spikes on the front, and metal studs on the sides.
To symbolize a Viking girl's maidenhood.
- If the franchise stayed true to known Nordic tradition, it can be assumed that the kransen had previously belonged to Astrid's Mother.