What are round red and white signs with a diagonal line?

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Tags

1. #prohibited
2. #white
3. #precaution
4. #viewer
5. #lights
6. #which
7. #shape
8. #depicts
9. #black
10. #amber
11. #behaviour
12. #signs
13. #yellow
14. #their
15. #alerts
16. #round
17. #environment
18. #prohibitory
19. #feature
20. #traffic
21. #through
22. #safety
23. #depicting
24. #usually
25. #picture
26. #thick
27. #diagonal
28. #warning