Yes I believe you can get a gauge by a rub. I look at size, reach(height), rap around(see if he is getting on the sides as well as the face), gouges and a pronounced rubline. The most important one is the pronounced rubline. I want to make sure he is routinely coming through the area to hit his rubs. Once I have found his rubline I look at the all other factors. Such as: height, quality, loaction, where he is going and coming from, etc.

Theories abound on this subject, but the 100% way is to catch him on film or by eye. That is why game cameras are so hot.