red flag law

Short definition from Wiktionary

Noun

1. 1
   A gun control law permitting police or family members to petition a state court to order the temporary removal of firearms from a person who may present a danger to others or themselves.
2. 2
   A law enacted in the late 19th century, requiring drivers of early automobiles to take certain safety precautions, including waving a red flag in front of the vehicle as a warning.