Wikipedia:Applause sign

Applause sign in television is an electrically illuminated sign which is turned on for short periods or is flashing on demand from show's producer during a live studio audience TV show to encourage audience members to applause. Modern applause signs might be simply a text that shows up in the monitors, which audience members see during the show. In the early television era, applause signs were made from cardboard and other materials which studio staff members showed to the audience to get required reaction.

Television tapings for sitcoms and talk shows have a warm-up comedian who warms up the crowd before the recording starts and sometimes in between the commercials or between the scenes. The warm-up comedian usually will familiarize the audience members with the Applause signs which are facing the audience near monitor screens. Before the show, the audience is given some training on how and when to applause and told to be loud and enthusiastic so that the people at home can hear them.

Applause signs are currently being used on late night talk shows including The Tonight Show Starring Jimmy Fallon, Late Night with Seth Meyers as well as variety and sketch comedy shows like The Price is Right, Saturday Night Live, The Daily Show among others''. ''