sign on the dotted line
在指定的地方簽字，表示同意或接受某個協議或合同
正式·簽署協議
英文釋義
to formally agree or commit to something, especially by signing a contract or agreement
例句
Just sign on the dotted line and the car is yours.
典故來源
源自合同上虛線標注簽名處，象征正式承諾。