Use the USPTO's TESS database.
- Start at http://www.uspto.gov
- Click on "search trademarks (TESS)"
- Click on "Structured Form Search (Boolean)" (provides more search options than the "Basic Search" mode).
- Type in the name of the owner or company, keeping in mind that a person's name might be indexed in a variety of ways. If the company name is more than one word, enclose the name in quotation marks. If the name has special characters, such as apostrophe, like as "John's", enclose in quotations.
- Select "owner name" as the field and perform your search.