sign的過去式是signed。
sign例句有如下：
1.Saying?No is?not?a?sign?of?weakness,?it is an?indication?that?you?know?your?own?strengths?and?are?able?to?prioritise.說“不”並不證明妳無能，說“不”可以反映出妳知道自己的能力何在而且懂得優先考慮。
2.I?can?sign?a?contract?up?to a?year.?I?don't know?where?I'll?be?after?that.我能簽最多長達壹年的。我不知道壹年後我會在哪裏。
3.If?you?often?hear?others?say?the?word?"naive"?,?it's a?dangerous?sign?that your?imagination?is?about?to?leave?you.如果妳對別人經常說“幼稚”兩個字，這就是妳的想象力即將離開妳的危險信號。