Very impressive quoting the rules and Merriam Webster however perhaps you should have read my original post.  I said that I always mark my ball but only mark it on one side.  I was wondering if others did that or if they marked it on both sides as my friend claimed was the correct way.  

Based on all of the responses I have read I intend to mark my ball on both sides from now on.  Thanks to everyone that responded.  

Tin Cups!! I use several of them depending on what makes me smile on a particular day. I've never run across a duplicate on any course I've played. If you need a line on your ball, use that too, but I generally turn a paw print up, smile, relax, and sink the putt. They have many designs to choose from, and it's a quick way to mark your ball and beats heck out of plain old dots-- The USGA does not require, but encourages you to mark your ball.

After hiiting the wrong ball during a tournament, I was determined to never let that happen again. I mark my Titleist with a blue putting line and I put my last name initial four times on the ball. It looks a little "cheesy" but I can always identify my ball without a problem.

I  mark mine under  the  number with a red mark skip 1 dimple and a  blue mark for the  great red,white and blue on both  sides. 

I mark mine with 6 red dots on both sides.  Even with all these dots people still play my ball and never look at it.

He makes a fine point, but the rules allow you to mark and lift your ball for identification - if you're in a bunker or something you're only allowed to remove enough sand to identify the ball and then you have to re-create the original lie as close as possible.

I only mark my ball on one side. 3 dots just right of the brand name and my first initial after. I always like to put my initials somewhere on the ball because so many people just use dots and I don't like loosing golf balls to people just because they can't find theirs and mine looks similar. 

I am with you on using more than just dots to mark your ball.  We all probably have a story about someone playing our ball.

Last year, I pushed a drive into the adjacent hole's rough.  Without checking, a guy went ahead and hit my ball into a greenside bunker.  After arguing with the guy, I picked up the bunkered ball and pulled a second ball from my pocket to compare both balls' marks [my first initial and a dot left of the number].  Only then did he consider that he MAY have hit the wrong ball.  We walked back and found his swoosh ball about 30 yards away!   Dude; at least know what brand of ball you are using!

Talk about angry!

My moral is to 1) keep the ball in play and 2), make sure to mark each ball before leaving for the course.  I had only marked that ball just before the tee shot!

Lots of good advice here.

I'll echo the statement that the more unique the markings, the better. To avoid somebody else playing my Titleist, at the first hole, I'll tell my playing partners exactly how I mark my ball. It may change depending on what color marker I have or if I lost the last one I played but it's usually two orange dots on either side of the number and one dot over the first "i' in Titleist.

Obviously you've already seen that you don't have to mark your ball, its just a good idea.  I lost a club championship because i played the wrong ball because are markings were so similar . 2 holes later we both played one anothers ball and i ended up losing by 1 stroke.  Tough loss, but i always mark my ball with a weird color now to avoid an confusion.

I am a Tin Cup fan and even tho it takes a bit of time for each dozen Velocities, I mark them with an American Eagle (red & black) on one side and an American Flag (red & blue) on the other side.  That way, it's obvious to my entire foursome which ones are mine!

Those are cool!!  I use a dolphin, whale tail, and a paw print on mine-- LOVE the eagle!!

ML Duffy

I mark my ball on both sides with a red dot on the left side of the number, and a blue dot on the right side.

I mark mine with a black dot above and below the logo on each side of the ball.

It is simple and not distracting when I look down at it.

One blue dot as centered as possible directly above the Titleist logo on both sides.  No one in my group uses blue ink, so it works for me.  I prefer it to be clean.