sign on the dotted line
在指定的地方签字，表示同意或接受某个协议或合同
正式·签署协议
英文释义
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.
典故来源
源自合同上虚线标注签名处，象征正式承诺。