What does the symbol of the mockingbird represent?

Mockingbirds in the book "To Kill a Mockingbird" represent people.

Here are some characteristics of the person that is like a mockingbird.

*Nice

*Can only do good

*Not a pest

*Easy target

People in the book that they resemble

*The black Man (I forget his name) that Atticus is defending

*Mr. Aurthur/ Boo Radley

*More