Final answer:
The letter 'R' appears next to the statement 'under 17 requires accompanying parent or adult guardian', indicating an R-rated movie with content suited for adults.
Step-by-step explanation:
The letter that appears next to the words "under 17 requires accompanying parent or adult guardian" is R. The R rating is issued by the Motion Picture Association (MPA) in the United States for movies. This rating indicates that the film contains some adult material and parents are urged to learn more about the film before taking their young children with them. An R-rated movie may include strong language, violence, sexual content, or drug use, which is considered inappropriate for children under 17 years of age without the accompaniment of a parent or adult guardian.