signature tune
noun [ C ] uk/ˈsɪɡ.nɪ.tʃə ˌtjuːn/ us/ˈsɪɡ.nɪ.tʃɚ ˌtuːn/
（某个广播电视节目开始或结束时或某表演者出场时播放的）信号曲，开始曲，结束曲
a short tune used in broadcasting at the beginning and/or end of a particular programme or to mark the appearance of a particular performer