Symbolism, Imagery, Allegory
You know what's guaranteed to be chock full of symbolism? A family crest. After all, their main purpose is pretty much to announce how cool and powerful a family is—and the Hapsburgs' crest is no different:
Alek looked out at the stormwalker crouched in the courtyard. On its breastplate was his family crest: the double-headed eagle devised of mechanikal parts. As he was growing up, the symbol had always surrounded Alek—on flags, furniture, even the pockets of his nightgown—assuring him of who he was. But now it only filled him with despair. (21.30)
You know what else is double-headed in a way? Alek's family. He's got his royal dad and his non-royal mom. And instead of their union following the traditional (read: natural) path, they've forged a non-traditional (read: constructed—or mechanical) marriage. Funny how fitting the Hapsburg crest is given how resistant the family line was to Franz Ferdinand's decision to marry Princess Sophie.
Even as he escapes, Alek carries the Hapsburg crest with him on the walker's breastplate and stamped on the gold bars Volger carries aboard. The crest's most momentous moment comes though, when he stands in front of it during the battle with the German zeppelins:
Then Alek realized where he was standing—right in front of the walker's breastplate, the Hapsburg coat of arms proclaiming exactly who and what he was… (33.37)
The Hapsburg crest is a symbol of Alek's family, and Alek's family is a pretty big deal in this book. In some ways, they're the people Alek loves to hate. He's forever cut off from everyone but his parents because of his mother's non-royal blood, and yet he's continuously trying to be accepted by the Hapsburgs as one of them, even though we suspect that Emperor Franz Joseph, his great-uncle, was behind the attacks on his parents and is actually trying to kill him. Being unable to avoid the crest, then, mirrors how haunted by his family legacy Alek is.
In one of the book's final scenes, Volger and Alek throw the gold bars—and the seal along with them—overboard as the Leviathan struggles skyward ahead of a German attack. They hang on to one bar, but even so, we think this is a pretty significant moment symbolically, and the moment when Alek really begins to form a new identity outside of his troubled relationship with his family. He throws the crest overboard, literally and metaphorically lightening his load.