The ham suit seems a bit ironic, at least. Scout is asked to be in the play and expressly told that she will have an important role. Her role, however, is just a ham that walks on stage at the very end of the pageant. There is some irony and humor in that.

The ham suit does make it difficult for Scout to move around and clearly see what's going on, but I suppose that couldn've been done with many other types of costumes.

I think it's really just a comment on the sillyness of life that we see sometimes. After all of the ugliness of racism and hatred it's a moment to chuckle before we get the final act of violence. Scout has learned a lot and had to endure a lot, but for a moment we remember that she's really just a little kid. The ham suit emphasizes her youth.

I, too, have never thought that there was any significance behind the ham suit Scout wears at the end of the novel. The only thing the suit does, as stated by bullgatortail, is protect Scout from being hurt by Bob Ewell. Outside of that, after racking my brain if I ever missed something about the suit, I cannot think of any image or symbolism that the suit represents.

I see nothing symbolic about the ham costume Scout wears for the Halloween pageant. It is meant to be a humorous outfit, and one would expect Scout to "ham it up" while wearing it, but instead she falls asleep and is late making her entrance for her cue of "Pork!" It is an inadvertently funny moment, and Judge Taylor is forced to leave the auditorium, "slapping his knees." The chicken wire costume covered with brown cloth in the shape of a "cured ham" eventually saves her life, protecting her from the knife with which Bob Ewell tried to stab her.