Does the franchise you are looking at buying have a registered trademark?
TESS is the search engine for U.S. Trademarks. It contains more than 4 million pending, registered and dead federal trademarks. This web page offers the most selection of trademark searches.
To know if a franchisor has registered their trademarks with the U.S. Patent and Trademark Office, click the link below. The simplest way to search is to click "New User Form Search (Basic)" and then the name of the franchisor.