A sole proprietor is not required to adopt a fictitious, or assumed, name. However, if he does use a DBA, he may be required to register it with his state or county clerk. Generally, you cannot use a DBA that is already registered with another individual or company. It is important to know DBA registration rules that may apply to you. For example, in Michigan, sole proprietors must register their DBA. However, Tennessee does not require sole proprietors to register an assumed name.