Noticed that I had a suggestion to address remarking a ball on the putting green when the marker interferes with someone else's line of play into the hole. Word has it that two competitors almost came to blows regarding this issue in league play! Without further ado, I'll do so...
Happens a lot. We make a putt that finishes 2 feet from the hole. It looks like the type of putt you really want to read before you finish out and your fellow competitors are all waiting. You mark the ball, but someone else now finds that your ball marker is now potentially in the way of their line of putt and they ask you to move the marker left or right. What is the proper procedure?
The rules of golf are fairly flexible in regard to moving your mark, but the key as I read them is to move your mark in a certain order, and then to repeat in reverse when moving the mark back to the original spot to make sure you're going to be putting from the same spot. The one thing you don't want to do is move a ball marker and then putt from that new location - that'll incur a one-stroke penalty for playing from the wrong spot.
So, here's what I usually do. My fellow competitor asks me to move my mark (say it's to be moved to the right). I approach my coin and try not to walk on the competitor's line. I'll then place my end of my putter head to the right of the coin and in line with a tree or a bench or something I can refer to later. I then move my coin to the back end of my putter, place it upside down (this gives me a visual cue that reminds me that I have to move the marker before putting out) and remove the putter head. If my fellow competitor still feels the coin is still in the way, I can repeat the procedure and move the coin another putter-head length to the right, and I'll have to remember to move twice (maybe I'll stack two coins to remind me). When I go to replace my ball, I'll put the putter head back on the green in line with my tree or bench, move my marker to the front of the putter head (and I'll repeat again if someone asked me to move it the distance of two putter heads). Once the marker's back down where the ball is supposed to be, you can place the ball in front of the marker and remove the marker.
I'll give you another option that's perfectly acceptable. Your ball is still sitting on the green. Instead of placing a marker behind the ball and measuring from the marker, you also could place your putter head to the right of the ball in line with your tree, post, bench, etc. and pick up the ball and place it at the back end of the putter. You could then place a marker behind the ball and lift the ball. When it comes time to putt, place the ball in front of the marker, place your putter head to the left of the ball in line with your tree, post, bench, etc., and move the ball to the front of the putter head and the ball should now be back in the original position.
Sometimes forgetfulness can be our undoing.... "Bernhard Langer, needing a par at the last hole to win the 1999 Greg Norman Holden Classic tournament at Lakes Golf Club in Sydney, Australia took a double bogey five to lose by one shot to Michael Long of New Zealand. There is nothing truly remarkable about that as many tournaments are lost or won at the death. However, in this case Bernhard Langer lost because of a simple mistake at the short 18th. He picked up his ball marker without first putting his ball down and by doing so he incurred a one stroke penalty. He describes it as the dumbest thing that he has ever done on the golf course."
Side note: When your ball is on the green, the player always has the option to mark his ball. If the ball is not on the green and interferes with a fellow competitor's play, he can ask you to mark the ball, but you must be asked in order to mark it. If you mark a ball when it's not on the green, do not clean the ball and replace it exactly when the mark is removed.