In 'Pulp Fiction', Jules is a character. Maybe a tee shirt could be related in that there could be a tee shirt with Jules' image on it, or perhaps Jules was wearing a particular tee shirt in the movie that became iconic in some way.
Well, in 'Pulp Fiction', Jules has a very distinct style. A tee shirt could be part of his overall look. It might be that a tee shirt he wore in the movie has now become a collector's item for fans of the movie. And his character's actions and dialogues in the movie are so memorable that anything associated with him, like a tee shirt, could hold significance.