Head-band. Hachimaki refers to any headband or sweatband worn round the forehead, often with a slogan inscribed. It is used in Shinto rituals of purification including matsuri where it is often worn with a happi coat. It has come to symbolise commitment, exertion, determination or sincerity (makoto) in a communal enterprise.
A Popular Dictionary of Shinto. Brian Bocking.