You may conduct a search free of charge on the USPTO website using the Trademark Electronic Search System (TESS) If your mark includes a design element, you will have to search it by using a design code. To locate the proper design code(s), please consult the Design Search Code Manual.
You may also conduct a trademark search by visiting the Trademark Public Search Facility, between 8:00 a.m. and 8:00 p.m. at Madison East, 1st Floor; 600 Dulany St.; Alexandria, VA 22313. Use of the Public Search Facility is free to the public. You can also conduct a search at a Patent and Trademark Depository Library near you. For locations, click PTDL.
Source: Trademark FAQ
