Perhaps face paints would be more appropriate. By what I have read consensus is Vikings did have tattoo's but I like the idea of face paints more.

Small google search yielded this: In Viking culture, Viking face paint was often used as a form of war paint, to intimidate enemies and show support for a particular cause or leader. Face paint was also used for religious or spiritual purposes, as some Vikings believed that it had the power to protect them or bring them good fortune.

So perhaps the face/body paint could be used for temporary buffs. Getting Wet would degrade the paint, eventually washing it off. After playing Assassin's Creed: Valhalla it feels weird not seeing any type of paint/tattoo's on my character.