directional vs turn signal

directional

noun
  • Something that indicates direction, such as a vehicle's turn signal. 

adj
  • Indicating direction. 

  • Of or relating to guidance or help. 

turn signal

noun
  • each of the flashing lights on each side of a vehicle which indicate a turn is being made to left or right, or a lane change etc. 

How often have the words directional and turn signal occurred in a corpus of books? (source: Google Ngram Viewer )