Effective in 1952, the United States Golf Association and the R&A--the two governing bodies of golf--changed the rules to allow marking a ball on the putting surface. Prior to 1952, if a golfer's ball was in your way (called a stymie), you had to putt around it or pop your ball over it.
Rule 20-1 of the Rules of Golf states: "The position of the ball to be lifted should be marked by placing a ball-marker, a small coin or other similar object immediately behind the ball."
Markers are as simple as a plastic circle with a prong that sticks in the ground, to metal discs with designs that can include a golf club's logo, a favorite sports team or a flowered design.
Golf ball markers typically range in size from that of a dime to that of a quarter, but the rules do not specify a size. Some golfers use a small button attached to their golf glove for that purpose.
The provision regarding golf ball marker type in the Rules of Golf is a recommendation, so the golfer is not penalized if she uses a different method of marking the ball.
The golfer can use a tee, a divot tool, a stone or even a leaf to mark his ball, but he cannot use an existing mark on the ground, such as a blemish on the green.