These are selected public libraries that house the CASSIS database containing all existing and pending federal trademarks maintained by the U.S. Patent and Trademark Office (USPTO). Beware that the these databases may be up to three months old before receiving updates from the USPTO. While they are usually free, there can sometimes be lines to get onto a host computer in the library. Alternatively, the USPTO now has available a searchable database over the Internet (still not timely updated). You can check their database at http://www.USPTO.GOV/tmdb/index.html.