Trademark law only applies to marks that are being used as a “brand identifier.” This means anything that identifies where your goods or services come from can qualify as a trademark and earn legal trademark rights.
In order to qualify for rights, though, the mark needs to be used for the purpose of identifying where the goods or services are coming from, and not just as decoration. For example, a Mercedes symbol on a Mercedes car would be a brand identifier because it’s signaling what brand of car it is. However, if a t-shirt were printed with Mercedes cars and logos on it, it likely would merely be decoration, and not a signal that the t-shirt was made by Mercedes.
Brand names and logos tend to be the most common marks used as brand identifiers, but other things can also be used. For example, the following have all been found to be valid trademarks because they identify the brands they are used by: sounds (NBC chimes, MGM lion roar); colors (UPS brown, Tiffany blue); mascots (Geico gecko); slogans (Just Do It); and product shapes (glass Coca Cola bottles; iPod).
