BEST-SELLING author John Grisham has joined Dickens, Shakespeare and other writers whose success has been certified with that most American of literary tributes - the T-shirt. But he is not terribly excited. ''I have not seen this particular garment. I have no plans to purchase one either,'' he said. He gave Barnes & Noble Inc permission to use a caricature of him. The US$12.95 (about HK$100) T-shirt is one of 15 in the bookstore company's line of shirts portraying classic and contemporary authors. Michelle Repass, manager of a Barnes & Noble store in Memphis, said: ''We use caricatures of various authors throughout the store, and he's been doing so well decided to add him to the line-up.''