A sign language is a way of communicating by using the hands and other parts of the body. In above picture staff is practicing how to say thankyou by using sign language.
In sign languages use of hands is a practice and it is understood with the eyes. We learned sign language mostly the sign, how to greet our guests.
Any means of communication through body movements, especially with the hands and arms are used when spoken communication is impossible or not desirable.
接客の手話を学ぶ旅館「八景」の従業員たち Employees of Hakkei learning sign language