Complex sentence: A person wearing a collar to symbolise their relationship with another is said to be collared--some people conduct formal "collaring ceremonies" which are regarded as effectively solemnising their relationship in the same way as a marriage ceremony.
Split into simpler sentences: A person wearing a collar to symbolise their relationship with another is said to be collared. Some people conduct formal "collaring ceremonies" which are regarded as effectively solemnising their relationship in the same way as a marriage ceremony.