What are the USGA Rules on Identification marks on balls?
USGA Rule 12-2: Identifying Ball
The responsibility for playing the proper ball rests with the player. Each player should put an identification mark on his ball.
If a player has reason to believe a ball at rest is his and it is necessary to lift the ball in order to identify it, he may lift the ball, without penalty, in order to do so.
Before lifting the ball, the player must announce his intention to his opponent in match play or his marker or a fellow-competitor in stroke play and mark the position of the ball. He may then lift the ball and identify it, provided that he gives his opponent, marker or fellow-competitor an opportunity to observe the lifting and replacement. The ball must not be cleaned beyond the extent necessary for identification when lifted under Rule 12-2.
If the ball is the player's ball and he fails to comply with all or any part of this procedure, or he lifts his ball in order to identify it when not necessary to do so,
he incurs a penalty of one stroke.
If the lifted ball is the player's ball, he must replace it. If he fails to do so,
he incurs the general penalty for a breach of Rule 12-2,
but there is no additional penalty under this Rule.
Note: If the original lie of a ball to be placed or replaced has been altered, see Rule 20-3b.
*Penalty for Breach of Rule 12-2:
Match play - Loss of hole; Stroke play - Two strokes.
*If a player incurs the general penalty for a breach of Rule 12-2, there is no additional penalty under this Rule.