How to Mark a Golf Ball on the Green

This comes directly from Golf.About.Com; And was written by Brent Kelley

The phrase "marking your ball" can refer to writing or drawing something on the golf ball for identification purposes, or it can refer to placing a ball marker on the ground to mark the ball's position while you lift the golf ball. It's meaning No. 2 that we are concerned with here - specifically, marking the golf ball on the putting green.
Unlike other areas of the golf course, on the putting green you can lift your ball for any reason. But you must always mark the ball's position when doing so. Some reasons to lift a ball when on the putting green:

• a) When you want to clean the ball;
• b) When you want to align the ball's graphics with your putting line;
• c) When you believe your golf ball might be in the way of another player, or a distraction to another player;
• d) When another player asks you to do so.

Marking the golf ball on the putting green is a common occurrence. So you better know the correct procedure.
Step 1
Place a small coin (or similar ball marker) directly behind your golf ball on the putting green.
Step 2
Pick up your golf ball. Important: Make sure your ball marker is on the ground before lifting the ball. Never lift the ball and then place a marker where the ball was. Place marker first, lift ball second!
Step 3
When ready to replace your golf ball on the ground, put it back on the green directly in front of your ball marker.
Step 4
Pick up your ball marker. As with Step 2, make sure you do Step 4 in the proper order. Which is: Place ball back on ground, then lift your ball marker.
And that's it. Pretty simple, eh?

Do I have to put my ball marker behind the golf ball on the putting green?
No, you are not required to place the ball marker behind the golf ball before lifting your ball on the putting green. You can place your ball marker in front of the ball or beside it, so long as you replace the ball in the correct position later. However, we recommend always placing the marker behind the ball. This is tradition, it's the way almost all golfers do it, and you'll avoid confusion by following the same convention.
Considerations and reminders
As with all activities on the putting green, be aware of other players' putting lines and be careful not to walk across another player's line.
Marking the ball on the green is addressed in the rules in Rule 16 and Rule 20. Failure to mark the ball before lifting it results in a 1-stroke penalty. If the ball is replaced in the wrong location (e.g., you place the ball down beside your ballmarker rather than in front of it) and you putt from that wrong location, it's a 2-stroke penalty. Different scenarios are addressed in the rules cited and linked above, so give them a read. But the easiest thing to do is to always remember to mark the ball before lifting, and always put the ball back in its correct location.

Related Article:
Are there any rules about what can - or can't - be used as a ballmarker?