Rubs are probably the only sign you can find in the woods that may denote a buck's size. Finding big rubs fires me up, depending first on when I find them and second, where I find them. Without visual confirmation you never know for positive they were done by big bucks but it's a pretty safe bet that there was one involved. I've seen bucks wearing out a tree during the heat of the rut and even late into the rut but for the most part I think they're done in the couple of weeks leading up to pre rut and into the beginning of the rut. Finding one at that time of the season may put you in the game. Finding one during the last couple weeks of the season usually only tells you that you should have found it earlier and it may be a good starting point next season. Whenever and wherever you find them tells you that at sometime, a buck used this immediate area in his traveling.
When, where, and why? Three questions any deer hunter should ask himself. The closer he can come to answering any of them the closer he is to tagging that buck. Related to rubs, and as I've posted on here in the past, it's my belief that a buck does most of his rubbing after exiting his bedding area rather than returning towards it. They may bed down anywhere but in some places, especially if they are unpressured, they may have a consistent bedding area. Generally, a buck moves in a more hurried fashion returning to bed than he does leaving it, thus he's more inclined to rub more during his slower mode after rising from bedding. With this train of thought and particularly in linear rub lines, "most of the rubbing I see I determine to be going away from his bedding area". Consequently, with bucks beginning their movement patterns at nightfall, most rubbing will be done under the cover of darkness. Backtracking those rub lines should put you closer to his bedding area. Big rubs; possibly a big buck.
When a buck rises from his bed he heads in a certain direction pointing him either towards a food source or potential does for breeding. In between there and those areas is where most of the rubbing is done. Rubs, and the timing of those rubs surrounding food sources may denote how and why they are made where you find them. Prior to the rut, finding them inside cover surrounding food sources more than likely signals that area as a food source for the buck himself. Once the rut starts, finding fresh rubs in those same areas leans more towards an area the buck travels in search of does. In either case, hunting the interior of the surrounding cover is probably a better idea than hunting directly over the immediate food source. Again, big rubs; possibly a big buck.
Timing, direction of travel, and location are 3 considerations. Another might be consistency from year to year. A big buck survives by staying alive. Once he finds a security area that meets that need he may very well "seasonably" return to that area yearly. Finding those last year's rubs in those areas may possibly be a starting point of interest the following year.
Linking rubs to their timing, distinctive tine markings, the prevalent wind directions during that time frame, and any possible likely travel corridors could very well aid to the perfect stand placement. Lastly, big rubs; possibly a big buck.
