用作名词，表示"符号"标牌“手势”迹象”等均为可数名词。如: We hung a sign on the door.我们在门上挂了一个招牌。 He gave me a sign to leave the room.他示意我离开房间。 There are signs of sales increasing.有迹象表明销售额在增长。
用作动词，表示"打手势"，可用作及物或不及物动词。 The policeman signed me to stop. The policeman signed to [for] me to stop. 另外还可以表示"签(名) “或. 上签字”，也可以是及物或不及物动词。 Have you signed (on) the cheque? 注:表示签名时，sign 只用作动词，不用作名词。其相应的名词为signature。如: The document bore his signature.这份文件有他的签字。 We need signatures and we haven't got enough of them.我们需要签名，而现在得到的还不够。