Question: How are beach volleyball block signals hidden from the opposing team?
About the article "Beach volleyball", section "Block signals".

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Beach volleyball players use hand signals to indicate the type of block they intend to make.
Block signals are made behind the back to hide them from the opposing team.
They are usually given with both hands by the serving player's partner prior to the serve, with each hand referring to the type of block that should be put up against an attack from the corresponding opponent.
A player may also "wiggle" or "flash" one block signal to indicate which opponent to serve to.
If the server is the designated blocker, he or she may run up to the net to block after serving.
Otherwise, the signaling player will perform the block.
Block signals may also be given during a rally while the opposing team is preparing their attack.
 Closed fist No block should be attempted for the opponent on that side of the court, also known as "pull-off" One finger The blocker should block an opponent's "line" attack, or a ball hit toward the nearest sideline Two fingers The blocker should block an opponent's "angle" attack, or a ball hit diagonally from the net and across the court Open hand The blocker should block "ball", deciding how to block based upon the opposing team's set, and the hitter's approach and arm-swing technique.
Common block signals.
Note: In Europe closed fist and open hand signals have the opposite meaning of blocking.
If the partner is showing the closed fist the blocker should block "ball" and open hand means that the blocker should "pull-off" the net. 
Rules and gameplay.
Rule differences between beach and indoor.
Beach volleyball is fundamentally similar to indoor volleyball: a team scores points by grounding the ball on the opponents' court, or when the opposing team commits a fault (error or illegal action); consecutive contacts must be made by different players.
The major differences between beach and indoor volleyball are: Playing surface – sand rather than hard court The dimensions of the court are 16 by 8 meters, compared to 18 by 9 meters in the indoor game.
The beach court has no "attack line", unlike the indoor court, which has such a line 3 meters from the net.
Team size – two rather than six, with no substitutions allowed Scoring system – best of 3 sets played to 21 (15 for a deciding set) rather than best of 5 to 25 Overhand touches and tips – open-hand dinks are illegal  A block at the net counts as one of the three allowed touches in the beach game, but not in the indoor game Open-hand setting standards are different in the beach game –double hitting is called tighter but lifts are slightly more lenient Coaching during matches is not allowed There are no rotation errors on the beach – players may switch sides at will It is legal to cross under the net in beach volleyball as long as it does not interfere with opponents' play Teams switch ends of the court every seven points, rather than between sets There is no Libero in beach like there is in indoor The only similarity in the courts used in the two forms of volleyball is the net.
In both versions, the height of the net is 2.43 meters for men and 2.24 meters for women. 
Kjell Schneider (born October 4, 1976 in Kiel) is a beach volleyball player from Germany, who won the bronze medal in the men's beach team competition at the 2005 Beach Volleyball World Championships in Berlin, Germany, partnering Julius Brink.  
In the game of volleyball, the act of digging describes a pass of a hard-driven ball from the other team.
In other words, digging is the act of stopping the ball from hitting your side of the court after the opposing team has either spiked or served it to your team.
Digging is a prolific term of volleyball jargon in both the indoor and beach volleyball communities.
Additionally, the term has gained some entry into the international lexicon through video games that use the term in their title.