"A trademark is a "word, name, symbol, device, or any combination, used or intended to be used to identify and distinguish the goods/services of one seller or provider from those of others, and to indicate the source of the goods/services." Generally, courts use a "likelihood of confusion" test to determine whether trademark infringement has occurred, i.e., whether a consumer is likely to be confused as to the source of the goods or services by the allegedly infringing usage.
Legally speaking, defending a mark is an important aspect of being a trademark owner. Besides the potential weakening and loss of distinctiveness ("dilution" in trademark speak), the failure to enforce a trademark could even lead to the forfeiture of some of the available remedies for infringement.
For this reason, multimillion-dollar companies hire professional watch services to monitor trademark use and possible infringement. And with the NFL, nothing seems to escape its notice—or legal wrath—which goes far beyond just counterfeiters.
In 2007, the NFL sent a warning letter to an Indianapolis church that had advertised a “Super Bowl” party and planned to charge admission for a viewing on a screen larger than 55-inches. The league has since loosened its policies regarding gatherings—the word “Super Bowl” and team names can be used—but still no admission fees are allowed. For churches, the event must be held in the usual place of worship as opposed to a rented space.
Notably, the logos of the NFL, the Super Bowl and the participating teams may not be used, which has led to rather hilarious if legally sound results. Take, for example, this promotional image by a Bethlehem, Pennsylvania arts campus, which features clip art, "Birds" and "Big Game," instead of official NFL logos, "Philadelphia Eagles" and "Super Bowl"..."