The rules of golf don't say that you have to put a mark on your ball, but it's a very good idea nonetheless.
Rule 6-5 states: "The responsibility for playing the proper ball rests with the player. Each player should put an identification mark on his ball."
Grabbing a Sharpie and adding your initials or a little smiley face could stop you playing the wrong ball, resulting in a lost hole in a match or a two-shot penalty in strokeplay.
You can also use marks on your ball to help your game, be it with a ring around the circumference to help you line up putts, or a straight line for you to aim down the fairway on tee shots.
Here's how some of the world's best players mark their golf balls...
Spieth marks his ball with a 'Z', which he says reminds him to "zero in" on his target. Interestingly, arguably the best putter in the game doesn't concern himself with an alignment aid to help him on the greens.
He plays with number four balls in round one, number three balls in round two, number two balls in round three, and number one balls for the final round, saying that "when I see that number one on the first tee, I know it's time to get to work". You big loony superstar, you.
Adam Scott says he's used the Southern Cross, the five stars depicted on the right half of the Australian national flag, for the last 10 years. He places the ball on the green blank-side up, enabling him to focus on using the putter as his alignment guide. Scott says he uses number two balls in pro-ams, but never in the tournament itself.
Louis Oosthuizen has a letter for each member of his family on the side of his ball, and a small dot next to the number. His caddie, Greg Hearmon, is the one who actually puts pen to urethane. Like Scott, Oosthuizen says he likes to look down on a blank white surface, so places his ball with the markings facing down and to the sides.
Bubba uses a bright pink pen, to match his bright pink Ping G driver, and draws a large circle next to the number. Watson uses the stamp on the side of the ball to line up to where he wants the putt to start, focusing on making a pure contact and getting the ball rolling straight end-over-end.
Fowler uses a plastic marker template to draw a straight line along the side of his ball which he then uses to line up putts. He adds an orange dot to help identify his ball, a habit that dates back to his college days.
Like Fowler, Stenson uses a plastic marker template to draw a straight line on the side of his ball. He says he used to use the line to line up putts, has since stopped doing that, but continues to add the mark nonetheless. He does use the line to point down the fairway on tee shots. The Swede says he normally plays high numbers: number five on the first day of a tournament, number six on the second, number seven on the third and number eight for the final round.
Poulter also uses a plastic device to draw a straight line, which he says he doesn't like to be too thick. Like Stenson, he uses the line as a guide on the tee, but not on the green.