The United States highway system has mile markers on both state and local highways, reports Wand'rly Magazine. Mile markers are small green signs with white numbers placed along the side of the highway to indicate the mile mark.
High traffic highways will have mile marker signs posted at one mile intervals, explains Wand'rly Magazine. Some interstate highways have mile marker signs posted at one-tenth mile intervals. Less traveled, back-country highways may only post mile marker signs every 20 miles. The number on mile markers increase when traveling north or east and decrease when traveling south or west. The number indicates the length of the highway in that state and resets when entering a new state.