The singer debuted a new tat over the weekend, which is plastered right on the side of his mug ... taking up a massive section, which almost runs up to his forehead. The tattoo depicts what looks a lot like Medusa -- the Greek monster with snakes for hair.

He also has the word "Love" scribbled across the top of his cheek -- very Post Malone-like, right? It's unclear who commissioned the new ink, but Aaron documented a good portion of the process on his social media ... and seemed to be in good spirits about it.

AC looked even happier riding around in the dirt on a quad sometime after the body artwork was done, captioning a video of himself with ... "Living my best life sweetie."

The obvious question that comes to mind ... you good, bro? Remember, Aaron just gave up his firearms this past week -- with proof, to boot -- and told us he'd be getting some treatment to kick Xanax. Now, he's drastically changed his appearance days later.

It's possible everything's fine and Aaron's just expressing himself creatively -- he was already blasted with tats before this. Then again ... a sudden face tat is usually startling.