Rated R for revolver?

Rihanna spent her Labor Day soaking up the sun and the surf in Hawaii.

The singer, 22, showed off her physique in a skimpy, turquoise bikini. Seen on her right thigh? Yet another tattoo -- this one of a life-size gun. Check out more hot pics of Rihanna in Hawaii.

The "Love the Way You Lie" singer already has over a dozen tats -- but a source close to the star tells Us this one's not real. Instead, the source explains, the temporary tattoo is for her role in the upcoming flick Battleship, shooting now.

Last month, Rihanna showed off new, bonafide ink on her neck which read "rebelle fleur" (roughly "rebel flower" in French).

On Tuesday, the star announced, via Rihanna Daily, the title of her upcoming new album: Loud. The new songs will be "sassy, fun, flirty, energetic," she said. "I'm just gonna be ME, cuz that's what you guys love the most, and that's what makes me feel best! Just being normal, normal for me is LOUD!"