CONCORD is comprised of a number of databases pertaining to Connecticut businesses. This link will bring you directly to CONCORD's trademarks database.
The USPTO's TSDR allows you to view all data relevant to the current status of a given trademark. You can search word marks by keyword, or use the Design Search Code Manual (linked below) to search image trademarks by design code.
This resource from the USPTO not only provides a comprehensive guide to every category of the International Classification system, but also provides explanatory notes and specific inclusions and exclusions for each class.
A design search code is a numerical code assigned to visual elements in a trademark design; for example, the design code for a five-pointed star is 01.01.03. This manual provides a searchable list of all design codes, and can be used alongside the TESS database (linked above) to search for design trademarks.
New to trademarks? Need to brush up? This page from the United States Patent and Trademark Office provides everything you need to know to start your trademark search.
This document from the World Intellectual Property Organization provides an exhaustive guide to the registration of international marks. Available in one large PDF or in smaller PDFs by section.
