Hrmm... after some research it appears I was wrong. I just assumed that they were a Zabrak thing since facial and body tattoos are a Zabrak thing and Sith Tattoos didn't exist until Darth Maul, coincidentally a Zabrak.
Edit: Further research leads me to believe that they were originally supposed to be a Zabrak thing, as it had already been established that Zabrak were into tattoos, but the writers of "Marked" the comic story(July 2005) where it was established that they were Sith Tattoos, also the first mention of the existance of Sith Tattoos, didn't realize that.