HTTYD THEORY: The meaning of Drago Bludvist's symbols?

Drago's ships are covered in mysterious symbols, but what do they mean?
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Tim Hickson
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SUBFURY ART COMPETITION GUIDELINES
1. Create a design for the t-shirt. This must include what you think a 'subfury' looks like. This can include Mishka (for example, a subfury might be a dragon/Mishka creature), or Mishka can be a separate thing in the design.
2. Send your design to [e-mail] (digital art and PNGs are preferable, but it's totally okay if you can't!)
3. Wait and see who the finalists are for the t-shirt! DEADLINE: Unconfirmed as of yet, but you will have till at least the middle of August.
I am so excited to see what you guys have made :D Thanks for watching subfuries.