One example of "loss of identity" is Scout's maturation from innocence to knowledge of course, but also with the slow evolution town itself. At the beginning of the novel, the town is portrayed as quaint, quiet and traditional. Tom Robinson's trial changes this when the town must confront that history. And this reveals the other side of their quaint town, which is one filled with racism, bigotry and inequality. This transformation of the town's shift in identity parallel's Scout's own loss of innocence. With Scout, it is learning to see the world from other's people's perspectives and of course, the harsh truth that the world can be unfair. The latter is something that every child knows even before they learn of the ignorance of some adults (i.e. the hypocrites and racists in Maycomb).
One of the moments when the town, as a collective group, comes to terms with the paradoxical tranquility and racism of its history is the outcome of the trial. But there is a striking moment that occurs when Atticus is guarding the jail to keep Tom Robinson safe. This is at the end of Chapter 15. Scout essentially defuses the tense situation and Mr. Cunningham gets the mob to go home. You can draw a number of conclusions about why Mr. Cunningham did this. Maybe he wanted to set a good example in front of the children, especially when Scout mentioned how she and Walter (Jr.) were friends; despite the different social classes they were from.
At any rate, this is a moment when a hateful group went to get Tom and thought the better of it. So, this is a small but significant shift in the town's identity from a quaint, tranquil town which passively accepts its racist history to a quaint, tranquil town which confronts that history.