Josh Brolin looks ready to join up with a “Gangster Squad” … because it seems he may have some expansive new ink on his back.

The actor was spotted surfing in Santa Barbara Saturday … and, while walking to and from the water, he pulled his wetsuit down to let his torso breathe.

And, on his back, is a huge black tattoo … with a lighthouse rising from the waves, topless mermaids framing the scene and the word “aretê” — an ancient Greek word that literally means “fulfillment” and “virtue ‘– squarely between his shoulder blades

It’s a stunning art piece — defintely bringing to mind Ben Affleck‘s colorful phoenix ink which took up his whole back, too.

It’s interesting because last year Brolin got a tattoo removed from one of his shoulders … thanking the company that did it for getting the “bulls***” off of him.

Brolin’s new ink looks real … and, we know he’s not totally against tats — because he recently gave his first tattoo, putting the ink on a fellow artist’s arm.