You can't tell the players without an endorsement card

Many companies in the activewear business sign sports personalities to promote their products and sponsor players in major sporting events to give their products visibility and credibility with the public. All segments of the industry participate, noting that when athletes wear their products on the field, it gives wide exposure to these products and lends authenticity to their use. Among the companies that spend heavily on such promotions are Fila, Nike and Reebok.
NEW YORK (FNS) - In the world of activewear, there's nothing like signing an athlete to an exclusive endorsement deal to build up and add authenticity to a company's brand. [...]