The Producers Guild of America’s plan to certify film credits is gaining traction.

The Producers’ Mark — a lower-case “p.g.a.” after a certified producer’s name — has been approved for 21 films with 39 producers. That’s triple the number of films and producers certified as of November, when Fox, Sony and Universal signed off on agreements to the voluntary certification process.

The mark was first used on the Weinstein Co.’s Prohibition drama “Lawless” when it screened May 19 at Cannes, followed by Mira Nair’s “The Reluctant Fundamentalist,” which opened the Venice Film Festival. “Silver Linings Playbook,” “The Magic of Belle Isle,” “Lonely Boy” and “Rise of Guardians” have also taken the mark.

Among the prominent new titles: Universal’s “R.I.P.D.” for Neal H. Moritz; Fox Searchlight’s “The Way, Way Back” for Kevin J. Walsh and Tom Rice; and DreamWorks’ “The Croods,” which Fox is distribbing, for Kristine Belson and Jane Hartwell. The mark has also been approved for several indie projects.

The PGA, which has more than 5,400 members, unveiled the producers mark concept in October 2010. More than 150 notable producers endorsed the mark to protect the integrity of the role of producer. To receive it, a producer’s work must be vetted and certified through the PGA’s arbitration process.

Producers don’t have to be a member of the PGA to be eligible to receive the certification, which is only given to producers who request it.

Other films with the mark include Lionsgate’s “All Is Lost” for Neal Dodson and Anna Gerb; Dimension’s “Dark Skies” for Jason Blum; “Plush,” for Blum, Catherine Hardwicke and Sherryl Clark; Universal’s “The Purge” for Blum, Sebastian K. Lemercier and Brad Fuller; “The Time Being” for Richard N. Gladstein; eOne’s “We Are What We Are” for Jack Turner, Linda Moran and Andrew D. Corkin; “Catskill Park” and “Generation Iron,” both for Edwin Mejia and Vlad Yudin; “Informant” for Stephen Bannatyne; “The Oyler House: Richard Neutra’s Desert Retreat”; and “Scribble” for Hal Schwartz and Ellie Kanner Zuckerman.