It really isn't worth the time, I don't think; however, it is < followed by sub followed by >. To turn it off, it is < followed by / followed by sub followed by >. Most of the students and most of the volunteers know that a number directly following is subscript. For superscripts we use the caret ^. And those work fairly well. I used the real subscripts because I thought that particular part of it would make it easier to understand.
