These are the referees' official hand signals when they are officiating a game of volleyball. If you want more detailed information, the full volleyball rule book can be found here. 

Point Awarded

Whenever a team successfully scores a point, the referee lifts their hand in that direction. 

Ball in

Whenever the ball lands inside of the lines on the edge of the court, or touches the lines, the referee points the arm and fingers toward the floor.

Ball Out

Whenever the ball lands completely outside of the boundary lines, touches the antennae or another illegal object, the referee raises the forearms vertically, hands open, palms towards the body.

Catch

If the ball is caught and/or thrown, the referee slowly lifts the forearm, palm of the hand facing upwards.

Double Contact

If a player hits the ball two times consecutively, not including off of a block, the referee raises two fingers, spread open

Four Hits

If a team hits the ball four times before returning it, the referee raises four fingers, spread open.

Net Touched by Player

If a player touches the net during play, the referee indicates the relevant side of the net with the
corresponding hand

Reaching Beyond the Net

If a player touches the ball or an opponent in the opponent’s space before or during the opponent’s attack hit, the referee, places a hand above the net, palm facing downwards.

Penetration under the Net

Either for penetration into the opponent court by a player (pictured), ball crossing the lower space, the server touches the court (end line) or the player steps outside his/her court at the moment of the service hit. Referee points at the place where the fault occurred.

Ball Touched

If the ball touches a player and subsequently lands on the ground on their side of the court,the referee brushes with the palm of one hand the fingers of the other, held vertically.

Attack Hit Fault

When a back-row player steps on or beyond the attack line when jumping or when a libero performs an overhand finger pass by the in his/her front zone or its extension to set the ball to a team-mate. Referee makes a downward motion with the forearm, hand open.

Blocking Fault

If a player makes a blocking fault, the referee raises both arms vertically, palms forward. 

Service Order Fault

A service order fault is committed when the service is not made according to the service order, the referee signals by making a circular motion with the forefinger. 

Double Fault and Replay

If two or more faults are committed by opponents simultaneously, a double fault is called and the rally is replayed, signaled by the ref raising both thumbs vertically. 

Delay Warning

If a team performs an improper action that defers resumption of the game, the referee covers their wrist with a yellow card. 

Delay Penalty

If a team performs an improper action that defers resumption of the game twice or more in one match, the referee covers their wrist with a red card and a point and service are given to the opponent. 

Misconduct Warning

If a team member performs incorrect conduct towards officials, opponents, teammates or spectators, they are shown a yellow card as a warning. 

Misconduct Penalty

The first rude conduct in the match by any team member is penalized with a point and service to the opponent. The referee signals this by showing a red card. 

Expulsion

The first offensive conduct by a team member, or the second rude conduct, is sanctioned by expulsion with no other consequences. The referee signals by showing both cards jointly. 

Disqualification

The first physical attack or implied or threatened aggression, or the second offensive conduct by a team member, or the third rude conduct, is sanctioned by expulsion with no other consequences. The referee signals by showing red and yellow cards separately. 

End of Set or Match

When a team wins 25 points in a set with a minimum of a 2 point lead, or 3 sets, the referee crosses the forearms in front of the chest, hands open. 

Change of Ends

When the teams are required to switch ends of the court.  Referee switches his left and right hands front and back as shown in the picture.

Challenge Request

When either of the teams or the referee wishes to defer to the video Challenge system to determine the outcome of a point.  Referee draws a rectangle with the hands.

 

Ball Not Tossed or Released at the Service Hit

If the ball is not hit with one hand or any part of the arm after being tossed or released from the
hand, the referee lifts the extended arm, the palm of the hand facing upwards. 

Time-out

When a team requests a 30 second time-out.  Referee places the palm of one hand over the fingers of the other, held vertically (forming a T) and then indicates the requesting team.

Substitution

When a player on the court is replaced by one from the bench.  Referee makes a circular motion of the forearms around each other.