The drawing has nothing special. There isn't any meaning nor inspiration apart from what it's drawn. A demon and an angel copulating (yes, I became refined at this hours, shit). This is it. Maybe it can remember to an specific scene of The Preacher (note: if you haven't read this comic, I recommend that you do it). Or maybe it's only a recurring theme...who knows.
Maybe you don't care about it (and I assume), but I'll be doing a tattoo course in april. It's what I've been looking forward to for some years. Can't wait to inject ink to people.