I live in a very old town which is surrounded by beautiful w

I live in a very old town which is surrounded by beautiful woods
I found a sign which said.(应该还有内容)
1.这两句的which都不能省略.
2.I live in a very old town which is surrounded by beautiful woods 句中的which=a very old town,
which在定语从句中做主语,不能省略.
3.I found a sign which said.(应该还有内容).此句中的which=a sign.which在定语从句中也是
做主语,不能省略.

可以。但“which is”要一同省略。
which - 事务
who - 人
when - 时间
what - 事情（必须在从句中有相应的句子成分）
how - 方式

I live in a very old town which is surrounded by beautiful woods 中的which引导了一个定语从句，which在从句中作主语，如果省略则从句成分不全，不能省，但可替换为that。
I found a sign which said中的which也是同理

那得看宾语了，这里宾语是town，乡镇，后面解释说明是哪一个，所以用which用什么要根据句子的意思和修饰的词。who修饰的中心词是人，that和which是物