The Official Rules of Golf appear on the About.com Golf site courtesy of the USGA, are used with permission, and may not be reprinted without the permission of the USGA.

12-1. Searching for Ball; Seeing Ball
In searching for his ball anywhere on the course, the player may touch or bend long grass, rushes, bushes, whins, heather or the like, but only to the extent necessary to find and identify it, provided that this does not improve the lie of the ball, the area of his intended stance or swing or his line of play.

A player is not necessarily entitled to see his ball when making a stroke.

In a hazard, if a ball is believed to be covered by loose impediments or sand, the player may remove by probing or raking with a club or otherwise, as many loose impediments or as much sand as will enable him to see a part of the ball. If an excess is removed, there is no penalty and the ball must be re-covered so that only a part of the ball is visible. If the ball is moved during the removal, there is no penalty; the ball must be replaced and, if necessary, re-covered. As to removal of loose impediments outside a hazard, see Rule 23-1.

If a ball lying in or on an obstruction or in an abnormal ground condition is accidentally moved during search, there is no penalty; the ball must be replaced, unless the player elects to proceed under Rule 24-1b, 24-2b or 25-1b as applicable. If the player replaces the ball, he may still proceed under Rule 24-1b, 24-2b or 25-1b if applicable.

If a ball is believed to be lying in water in a water hazard, the player may probe for it with a club or otherwise. If the ball is moved in probing, it must be replaced, unless the player elects to proceed under Rule 26-1. There is no penalty for causing the ball to move, provided the movement of the ball was directly attributable to the specific act of probing. Otherwise, the player incurs a penalty stroke under Rule 18-2a.

PENALTY FOR BREACH OF RULE 12-1:
Match play — Loss of hole; Stroke play — Two strokes.

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.

©USGA, used with permission