Iron Armour Seal

This is the seal that keeps the Eight-Tails sealed inside Killer B. It takes the form of the kanji for on his right shoulder. The details of the seal is unknown, beyond the fact that it is stated to be lower-quality and weaker than the Four Symbols Seal, which contained the Nine-Tailed Demon Fox.

Trivia

 * In the manga, the seal is depicted as being black. In the anime however, the seal is blue.