Talk about taking action. Even when the Danes don't understand what they're trying to prevent, they still know they have to prevent it:
"We don't know where [the Germans are taking the Jews] and we don't really know why. They call it 'relocation.' We don't even know what that means. We only know that it is wrong, and it is dangerous, and we must help." (4.68)
And boy do they help. Nearly every Danish person we encounter in the book is committed to helping the Jews escape from the Nazis. Peter, Henrik, Mr. and Mrs. Johansen, and even young Annemarie are all fully committed to helping their friends and countrymen.
Wait, so if everyone is taking the same actions, how do these actions distinguish them? Well that's where exceptions come in. Think about the shopkeeper who's scared of the Nazis and doesn't step forward to help Annemarie when a soldier is questioning her. That one moment of inaction highlights the courageous acts of all of our main characters.
Okay, so maybe we should say prop—singular. But the Star of David necklace is important enough that it gets to be its own tool of characterization.
We get even juicier in "Symbols, Imagery, Allegories," but let's just say that this necklace is a symbol of Ellen's identity. When she has to take it off, removing it seems like an impossible task:
"'I can't get it open!' Ellen said frantically. 'I never take it off—I can't even remember how to open it!'" (5.42)
This prop—which is, let's face it, much more than a prop—truly defines Ellen. So when Annemarie wears it around her neck, she's keeping her friend close to her heart.
Annemarie and Ellen are physically opposite. Annemarie is tall and "lanky" (1.2) and Ellen is "stocky" (1.2); Annemarie has light blond hair and Ellen has super dark hair. But here's the catch: those things don't define them. The end.