Historically, there is not a lot of evidence that the Vikings used tattoos to express themselves, although some historians agree that they used to have tattoos depicting green trees from the tips of the fingers to the shoulders. Nowadays, the Vikings can be drawn both with an authentic or mythological representation.
For those who choose the first road, you should avoid pictures with horned helmets (the real Vikings have never used them ). Vikings used to dress in a very simple and practical way, when it came to weapons armor.
Even the elusive double-bladed axe has never existed, as they used an axe lighter and faster. What do people want to represent with a Viking tattoo? Surely strength and capacity of conquest.