For the National Association of Theater Owners, CinemaCon is an opportunity to discuss new audio technology, brainstorm about how to fight camcorder pirates and sample the latest and greatest in popped corn. This year, John Fithian, president and chief executive of that trade organization, also used the spotlight to complain about a glut of R-rated films.

He said attendance had suffered this year because of “the weight of too many R-rated movies.”

“Make more family-friendly films and fewer R-rated titles,” Mr. Fithian said. “Americans have stated their choice.”

Appearing with Christopher J. Dodd, chairman of the Motion Picture Association of America, Mr. Fithian also unveiled minor tweaks to the way ratings for individual films are advertised. The labels will include more prominent and legible descriptions of why a movie received a certain rating. Theaters will also begin running a ratings-related public service announcement.

Mr. Fithian’s criticism of R-rated movies comes after the school shootings last year in Newtown, Conn., and shootings last summer at a movie theater in Aurora, Colo.