Yeah thats what I've heard. I work at a moble home plant and some of us were sitting around and happened to notice the mark. Sence I posted the question I've heard a couple answers. One, something called a Fleetwood system where they use these marks for wall studs. They save one stud every 8'. Another was foor floor joist. As far as I can tell Stanley tape measures, 16' and up, are the only ones with this mark.