Diaz sported a gold ring with a thin band and sparkling stone set in a swirly setting on her ring finger at a recent luncheon celebrating a Hollywood Costume exhibition at the Wilshire May Company Building, the future site of the Academy Museum Of Motion Pictures, here.
It has been reported previously that Diaz and Maddem were "openly acknowledging to friends that they see a long future together, and yes, marriage may be a part of that plan".
Diaz was, however, also spotted wearing a thick yellow gold band on the same finger by itself at several events in early September in Germany and London to promote her comedy film "Sex Tape."
Diaz and Madden, 35, are said to have been dating since May and have been spotted acting 'cute' in public together several times. She introduced her beau to her parents in July.