Synonyms for Warning sign:

• n.

  •sign of things to come (noun)
  • premonition,
  • warning,
  • prediction,
  • signal,
  • portent,
  • handwriting on the wall,
  • harbinger,
  • sign.

• Other synonyms:

  •n.
  • foreshadowing,
  • preindication,
  • pre-indication,
  • foreshadowings,
  • handwriting on wall,
  • danger sign.