Johnny Depp Changes Amber Heard Knuckle Tattoo Again, SCUM to SCAM

Johnny Depp is throwing out all the rules on exes and tattoos, 'cause he's changed his Amber Heard-inspired knuckle ink yet again ... and added a dash of chaos.

Fellow Hollywood Vampires bandmember Tommy Henriksen posted a photo of Depp's infamous tat last week, showing the actor's changed his previously reworked SLIM-to-SCUM message to now read SCAM. He used the anarchy symbol for the 'A.'

What's kinda creepy about it is, the tat is still fresh and the scarring makes the red ink seem like a scab. You'll recall ... Johnny already changed the OG tat -- which initially read SLIM (his old nickname for Amber) -- to SCUM in the wake of their divorce.

Anyway, it's clear Johnny's still willing to bleed over Amber -- and over his art too.