signal slogan sign

三都的意思有很大的区别,只是形近而已
signal信号；暗号
EG：The firing of the gun was the signal for a chain of beacons to be lit.
开枪是接连点燃烽火的信号.
The policeman raised his hand as a signal to stop.
警察举起手,示意停下.
slogan 标语,口号,广告语
EG：The crowd chanted slogans and waved banners.
人群有节奏地呼喊着口号并挥舞着旗帜.
sign标记,标志；表示
EG：Flowers are often given as a sign of affection.
鲜花常用来表示爱慕.
The shops are full,which is a sign that the recession is past its worst.
商店里到处是人,表明经济衰退的低谷已经过去.