Huh, so that's the same model year as mine. I guess the marks must have worn off on the topsheet and been planed off on the sidewall?
So the easiest idea would be to take your skis into a shop that sells Kastle and has a 188 MX88 in stock and make a new center mark using one of their skis as a reference. I don't think they've changed anything aside from graphics in years (though someone can correct me if I'm wrong).
That being said, for what you're trying to do it's irrelevant. Assume the skis were mounted pretty much correctly and experiment with moving the binding position fore and aft. If you're going to experiment to find the best position, the factory line doesn't really matter.