Although not required prior to filing an application, you are encouraged to search the USPTO's trademark database to see if any mark has already been registered or applied for that is similar to your mark and used on related products or for related services. If your search yields a mark that you think might conflict with your mark, you should then check status to see if the application or registration is still "live," since any "dead" mark cannot be used to block a new application.
A complete search is one that will uncover all similar marks, not just those that are identical. In this regard, searching for trademark availability is not the same as searching to register a domain name. A domain name search may focus on exact hits, with no consideration given to similar names or use with related products and services. Basically, a domain address is either available or it is not. The trademark process, on the other hand, is more complex. As part of the overall examination process, the USPTO will search its database to determine whether registration must be refused because a similar mark is already registered for related products or services (i.e., even identical marks may co-exist if used on goods or services not considered to be related in any way).
**Please note that the USPTO does not offer advisory opinions on the availability of a mark prior to filing of an actual application.**
In addition to the videos found on the "Trademarks" page of this guide, the USPTO website has a great deal of information. Or, you may search the following: