The seashell that Peter Neilsen gives Annemarie represents several different things. Because it comes from the se,a it is a clue to the work that Peter had been doing and the adventure that Annemarie will take part in. A shell is also protection for a sea creature. The characters of Number the Stars must each find a way protecting themselves. Visually, the shell is also representative of the hidden appearances that come up through out the novel. A shell conceals something, but one cannot be sure just by looking at it what it might conceal. A shell is often full of surprises, just as the characters and events of the novel are.
The Star of David appears in several places during the course of Number the Stars. The Star of David is a central symbol in the Jewish tradition. In the novel, it represents the necessity for Ellen and all the Jews to hide their religion. Until the end of the war, Annemarie keeps the Star of David necklace that Ellen wears. The necklace symbolizes Annemarie's devotion to her friend and her stance against the Germans. Stars also appear in the psalm that Peter reads before the voyage to Sweden. In this case, the stars represent Annemarie's tainted view of the world. To her the stars demonstrate the vastness and hopelessness of existence.
The woods symbolize a right of passage for Annemarie. They operate as part of the theme of voyage and transformation. When Annemarie passes through the woods on her way to the boat, she is undergoing a transformation. She is discovering her own ability to do the job of an adult. For the Rosens, the woods are part of the passage from danger to safety.