The Dragonmark, formerly known as the Slavemark, is described as "the ultimate mark of shame in the Archipelago" in the ninth book, How to Steal a Dragon's Sword. It is given to mark one as a slave, and is impossible to remove. If someone is shown to have the slavemark, they are to be instantly banished from their tribe and forced to live in slavery forever. It looks like a thin dragon curled into the shape of an "S".
As stated in How to Seize a Dragon's Jewel, after Hiccup Horrendous Haddock I banished Merciless from the Barbaric Archipelago, he put the first Dragonmark upon his forehead as a sign of unity between humanity and dragonkind. The mark was made out of the combined blood of Hiccup the First and his dragon companion, the Wodensfang.
The mark acted as a symbol of the Kings of the Wilderwest and the dragon riders for around a thousand years until Grimbeard the Ghastly (once Speedfast), a new and young King rejected it and made it a symbol of shame and slavery. As a result Speedfast's generation too rejected the Dragonmark and eventually the older generation which bore the mark, became ashamed.
Speedfast grew up into the infamous Grimbeard the Ghastly, and had three sons. When his youngest son, Hiccup Horrendous Haddock II marked his forehead with the Dragonmark as a symbol of his affection towards his dragon-brother, Furious, Grimbeard tried to rub it off, but failed.
When Grimbeard murdered Hiccup the Second, the fall of the Kingdom of the Wilderwest was sparked. After Grimbeard destroyed the remains of his kingdom himself, he accepted the Dragonmamrk and put it upon his forehead, and sailed off into the west in The Endless Journey.
Over a year later in How to Steal a Dragon's Sword Excellinor the Witch reveals Hiccup's slavemark to the tribes of the Archipelago, banishing him from and sentencing him to slavery, along with his father.
A year later in How to Seize a Dragon's Jewel, Valhalarama gave the Mark to herself and renamed it the Dragonmark, saying it should be given to those who would follow Hiccup as their King. Soon many other Vikings accepted Hiccup and took the Mark.
In How to Betray a Dragon's Hero Wodensfang reveals to the Ten Companions of the Dragonmark the origins of the Slavemark and that it was originally called the Dragonmark.
Later, right before Snotface Snotlout's sacrifice, he accepted an "improvised" Dragonmark made by Hiccup out of charcoal dust, symbolizing his redemption.
Characters having the Dragonmark
- Bearcub's Grandmother
- Unidentified Wanderer slaves on The American Dream 2
- Hiccup Horrendous Haddock III
- The Hairy Scary Librarian
- Stoick the Vast
- Baggybum the Beerbelly
- Gobber the Belch
- Fishlegs No-Name
- The majority of the Hairy Hooligan Tribe.
- Numerous Dragonmarkers got the mark voluntarily, including
- Hiccup Horrendous Haddock II
- Grimbeard the Ghastly (at his death)
Eret has a scar on his chest, which Drago gave him for returning with no dragons. The scar could be a reference to the books, or possibly even a movie-verse Dragonmark, as it is a mark of shame, as the Dragonmark was, and also a mark of Eret's failure. But in the books, the Dragonmark was once something that all the Dragon Riders had, so readers of the books may consider this foreshadowing to Eret becoming a Dragon Rider.
In "Enemy of My Enemy", Hiccup was almost branded, which could be a reference to the Slavemark.