black flag

/B L AE1 K F L AE1 G/
noun
  1. 1

    A flag with a black color, used as a symbol of anarchism.

  2. 2

    A racing flag with a black color, used in auto racing to summon a driver to the pits.

verb
  1. 1

    To summon (a racing driver) to the pits by waving such a flag.

Source: https://en.wiktionary.org/wiki/black%20flag