My first example of an elk territory rub 

This is the number one thing I look for while elk hunting in thick timber. Bulls are highly territorial during the rut, and they mark the same tree several years in a row to let the cow know they are in the area. This isn't the greatest example, but it gives you an idea. I believe there are several types of rubs, such as scratch rubs that are very small where they had an inch while getting rid of velvet, velvet rubs where their pure intent is to strip the velvet, aggression rubs where they beat up saplings while waiting for their cows to come into estrus, and avoiding other bulls in the area, and territory rubs which signify it's their territory, and it also lets the cows wanting to be bred by that bull know they are in the area.