A classic Viking helmet morale patch - similar to the spagenhelm and Gjermundbu helmet styles made of bog iron, mind you, not the tv/movie version with horns.
Not that there's anything wrong with a horned helmet!
Viking Helmet Morale Patch
Size: 2.16" x 3" with hook fastener material sewn on the back.
This is just a little more realistic, though (via the National Museum of Denmark).