Before using a trademark, service mark or trade name, a trademark search should be performed to find out if anyone else is using a similar mark or name for similar goods or services. Otherwise, you may spend a great deal of money and time promoting your mark or name only to find out that someone else has prior rights. The last thing you want is to be on the receiving end of a lawsuit for infringement.
A proper search should investigate state and federal registrations, as well as unregistered uses. Remember, a registration is not required to establish trademark rights - they are generally based simply on use of the mark.