Lady Gaga -- Tattoo Homage to David Bowie

Lady Gaga hit up legendary tattoo artist Mark Mahoney Saturday night ... and walked away with a hefty David Bowie "Ziggy Stardust" on her side.

Gaga strolled into Mark's WeHo shop, "Shamrock Social Club." Gaga drew quite the crowd ... but it all went down behind closed doors.

The singer is set to perform a tribute to Bowie at the Grammys tomorrow ... and what a better tribute than one delivered with a portrait of his face on her body?