• Umpires should hold signals (out/good) for a few seconds longer than normal.  If you put your hand down straight away, and then a deaf player looks at you, they will miss the call.  If the player queries the call you should repeat the signal to confirm.
• Chair/central umpires should visually indicate calls that conclude the point, e.g. with a raised hand if the ball is out, flat hand to confirm that the winning stroke was good - this may involve repeating the call made by a linesperson.  This is for the benefit deaf spectators as well as players.
• When calling time, e.g. after players have been seated, wave to attract the player attention & then point at your watch.  Ensure player chairs and items such as umbrellas are arranged so that the central umpire can be seen by the seated player.
• Especially with two deaf players on court, both players may sometimes miss a call and play may continue.  From the chair, make the call and raise your hand, and wait patiently for the players to realise that a call has been made & stop play. 
• All calls should stand - do not think that just because neither player noticed the call that it should be ignored.
• If scoreboards are available, use them.
• Keep in mind that players in hearing competition may remove their assistive listening devices mid-match, e.g. due to sweat, rainy conditions, or comfort - so their apparent hearing ability may change.  This is not an issue in formal deaf tennis championships, because assistive listening devices are removed.  

Communications tips from various perspectives:

• General
• For coaches
• For competitors
• For officials
• For tournament organisers
• For clubs and venues
• and last but not least.... for deaf tennis players