You will find bucks make two types of rubs, normal travel pattern rubs that are rubbed on the side from which he approaches (and will all line up into a rub-line), and those that mark the outer edges of his range. The rubs along the outer edge of his range will be rubbed on the side facing the center of his range. If you drew them out on a map, the rubbed side would all point "inwards" to his range.
Field-edge rubs generally meaning nothing as they are usually rubbed facing into the field. However, if you find field-edge rubs not facing into the field, you've probably found one of the buck's preferred entry points into the opening.