About uniforms and belts
Uniforms have been used for centuries to indicate a person's affiliation with a certain group. The martial arts have their own unique uniforms that indicate affiliation with a style, organization, school, etc., but the uniforms also serve a utilitarian purpose; they usually make it easier for the wearer to train and participate in a particular art.
For as long as uniforms have existed, there has been some sort of identification on them to indicate the wearer's place within a groups hierarchy. The martial arts use belts, sashes, etc. to not only keep the uniforms closed but to also indicate the wears level of proficiency and place within the hierarchy of a style, organization, or school.