Well, Mirren, 65, takes her pal's private souvenir very seriously.
"I'm going to frame them and hang them over my bed," the Oscar winner told reporters at Saturday's Producers Guild of America Awards ceremony in Beverly Hills.
Brand, 35, who costarred with Mirren in The Tempest and the upcoming Arthur, has been vocal in his adoration of the actress. Mirren responds with equal praise for him.
"He's so cool," she says. "He's fabulous. We're really close friends. I wear the pin he gave me around my neck."
But when kiddingly asked by PEOPLE if Her Dameship thinks she'll someday be offered godparent duties to Brand and wife Katy Perry's kids, Mirren gave out a long chuckle and said, "I don't think so."