Having good manners is seen by many people as a sign of cult

Having good manners is seen by many people as a sign of cultural understanding and good taste.（1）这句话什么意思?（2）is seen说明是被动吗?（3）by、as、a sign of cultural understanding、good taste在这句话中该怎么翻译呢?查了字典,感觉里面的解释往里面套都不太像.