Oh, and what I classify as signpost rubs are large trees hit year after year - eventually signpost trees usually get killed from the deer rubbing them. A first time rub on a big tree I don't classify as signpost - but probably a single buck using the area.
Growing up in Ohio - when I had lots and lots of time and lots and lots of ground to hunt - I knew of a half dozen real signposts in the area. I periodically checked them through the season - when one started to get hit I'd get into the area for a couple of days at least. I killed a couple of good bucks within a day or two of certain signposts starting to get hit. One tree I still remember the day each year between 1988 and 1993 when that signpost first got hit. Yeah, I've got a problem
Signpost rubs (generally on cedar trees where I'm from) can be good to hunt. If there is a big scrape nearby, even better.