As seen on / worn by: Celebrities have long been a great source of Social Proof - especially when it comes to fashion. In this example, from the Van Halen Store, the site features pictures of Taylor Hawkins (drummer for the Foo Fighters) wearing their product.
In cases where celebrities are being used as Social Proof, the Halo Effect also comes into play - since the "halo" of their celebrity gives the product itself a little "borrowed sparkle."
Source: VanHalenStore.com