一、sign 名词。意思是“标志、符号、示意、信号”。通常指能发现或能看得见的实物。例如：

The sign on the wall said,“Now wash your hands.”墙上的牌子上写着，“请洗手”。

A red flag was placed there as a sign of danger.那儿插着一面红旗，预示着那儿危险。

He made a sign to me to leave the room.他打了个手势要我离开那间房。

二、signal 名词。意思是“信号、手势、（立即会引起某情况的）动作”。通常指暗示或表示的行动。例如：

The flash light was a signal that a train was coming. 灯闪烁是一辆火车开过来的信号。

She made a signal with her arm for a left turn.她打手势要左转弯。

His scolding was a signal for the girl to start crying. 他怒骂使女孩开始哭起来。

（新来的朋友：您不妨先我的头条公众号以便阅读往期讲座也欢迎您的点赞转发）