Nail polish remover or white spirit.
ball
everywhere ive been, yes
One ball is in the line of play of the other. No specific name for it really, just mark the ball and move the marker if necessary.
They mark their ball out of courtesy for other players as if one player on the green hits the ball of another they receive a two shot penalty. It is also so the player can clean his ball and line it up.
You can use nail polish remover to remove most permanent markers off a disc.
Ball markers are used in the game of golf. When the golf ball is on the putting green it may be lifted and cleaned or sometimes it must be moved to allow another player to putt. To remember where the ball is, a ball marker is placed behind where the ball was located. Ball makers can be any small flat object such a a coin or plastic counter.
You place a coin behind your ball, if they played away and hit your ball they would receive a two shot penalty- they would then have to play their ball as it lies and you would have to replace your ball.
I'd use a permanent marker. As you (carefully) count each one, color it in with the marker, to avoid counting any one twice and enabling you to know when you have counted them all.
Pin
A Golf Ball
Golf Ball