I'm using MEPIS, and I swear I found this too.
Not to get shot down in flames, but I was sure I'd changed the desktop wallpaper to something else... And then logged in to root one day to check my log files, and the wallpaper had changed to the skull & crossbones one!
Glad someone else has seen this too!
I couldn't see anything suspect in my logs, so decided I was just going crackers...
It's a story I'll tell my grandkids :/