The words pay homage to the murdered rapper Tupac, relating to the title of one of his albums and a tattoo he had across his stomach.
The 23-year-old star tweeted that she was having a “tat night” and was pictured lying on her front in the chair getting inked with a bottle of beer in her hand.
Instead of tweeting a tattoo she was pictured getting, she decided to tweet a pink Tupac tribute, but it is unclear whether this was made with a tattoo gun or a pen.
She tweeted along side the picture: “All these bitches screaming that 2pac back #THUGLIFE”.
Tupac was shot four times in a drive-by killing in 1996.
Rihanna also posted: “Tat my fuckin name on u girl so I know it’s real!!! #MINE”.
This alludes to We Found Love collaborator, Drake’s single Free Spirit, where he references Tupac’s girlfriend Kidada Jones, who had his tattoo on her arm.
It is thought Rihanna’s tattoo antics happened during her holiday in Hawaii last week, even though she only tweeted them earlier today.
Her tattooist Mark Mahoney has also inked Cheryl Cole, Britney Spears, Nicole Richie, Angelina Jolie and Brad Pitt.
Rihanna already has a music note tattooed on her ankle, a Pisces sign behind her right ear, the word “love” on her middle finger and stars on the back of her neck next to the words “rebelle fleur”.