I doesn’t matter if you think Snape is really reformed or not, the presence of that tattoo can’t be a good thing for him.
Originally, I assumed that this was Snape first noticing the reappearance of the mark, but then I though it would be cool if this was when Vol…He-Who-Must-Not-Be-Named
summoned all the Death Eater’s to him at the end of 4th year.
Yes, I know that the tattoo never glowed green, but come on it looks cool, plus I wanted some practice with color shading (i.e. on his face). I wouldn’t have been able to do that if I made the thing black, and I couldn’t really see the red glowing.
Snape © Rowling
Snape’s Lion Design © Kira617