Markings applied using a felt-tip pen are not contrary to Rule 4.2a(2).
Rule 6.3a encourages the player to put an identification mark on his or her
ball to help ensure that he or she plays their own ball throughout the round.
There are no regulations to limit what or how many markings can be applied
to the ball by the player, provided its original markings can be discerned.
Normally, only the Committees in charge of competitions involving expert
players (professional-level players and/or players at the highest levels of
amateur golf) should introduce a Model Local Rule requiring a player to
use a ball included in the List of Conforming Golf Balls, the penalty for
breach of the Local Rule being disqualification. However, if this Local Rule
is not in place, then the assumption is that a ball used by a player conforms
unless there is strong evidence to the contrary e.g. a player used a 1.62 inch
diameter golf ball (a ball which used to be in circulation and was permitted
under the Rules before finally being prohibited worldwide in 1990)
