What is the symbol the night King left?

Related questions

1. What does the White Walker spiral symbol mean?
2. Is Jon Snow brother to the Dragon Queen?
3. What episode does Jon Snow and Ygritte make love?
4. How did Dany get dragon eggs?
5. Why did ygritte shoot Jon Snow?
6. Why did Jon kill qhorin Halfhand?
7. Who did Jon Snow kill first?
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Tags

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2. #anything
3. #island
4. #queen
5. #which
6. #umber
7. #explained
8. #stands
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10. #lyanna
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12. #younger
13. #confused
14. #beric
15. #night
16. #dondarrion
17. #exactly
18. #westeros
19. #mormont
20. #served