Most states require a DBA -- a "doing business as" certificate -- if your business uses any name other than your own or yours and your partners' combined. If you create a living trust, the trust will also need a name. But since it isn't a business, it won't be a DBA. If you're the trustee, you can use a DBA for any businesses the trust owns.
Legally, you and your living trust are two separate entities, so your trust must have a name of its own. Theoretically, you could name it anything, but attorneys recommend something along the lines of "Your Name Revocable Trust." If the name is the same, banks and investment firms will be more confident and cooperative about transferring assets into the trust's ownership. If you change your name after you marry, for example, it's a good idea to change the trust name too, so that it's clear you're the person who created it.
DBA registration helps consumers track down the owners of a business if they need to. If you do business under your own name, as some self-employed individuals do, you don't need a DBA. If you do have a business name, you still may not have to register: In Florida and California, for instance, a sole proprietorship with your last name in the title, such as Smith Plumbing or Walpole Party Planning, doesn't need a DBA. A name such as 24 Hour Party Planning would require one.
Trusts Owning Businesses
A living trust can legally take ownership of a business and also of its DBA. With a sole proprietorship, you would transfer any assets and accounts the business owns to the name of the trust, and also place the DBA in the trust's name. If you're trustee, you could then continue to run your business as you always have. You may also be able to transfer your ownership share of a partnership or a corporation into the trust's control.
If you need to change your business name and refile a DBA, you, as trustee, can do that on behalf of a sole proprietorship the trust owns. You can also file if you set up a new business or subsidiary using trust assets. If the business is a partnership, a limited liability company or a privately held corporation, you may need the consent of your fellow owners to decide on a business name or any changes to the name.