Justin Bieber is not stranger to body ink, but on his face???!!!

The 21-year-old singer permanently marked his face with a teeny tiny cross next to his eye -- so small it's barely even visible in this Instagram photo Bieber posted on Sunday ahead of his concert date in Philadelphia, Penn.

Biebs got inked at West 4th Tattoo Parlor in NYC on May 6. Tattoo artist Jonboy told Us Weekly, "It represents his journey in finding purpose with God.” JB got the tat with BFF Joe Termini Friday night before his impromptu concert at nightclub Up & Down. This ads to his more than 50 pieces of body art, including a "Purpose" tattoo, in honor of his latest album.

At least this'll be an easy one for Dr. Tattoff to laser off ... it's so small!