is a specific kind of: sign, signal, signaling.

is a broader term that covers: watch fire | light | red light, warning light | flare, flash | flag, signal flag | air-sleeve, air sock, drogue, sock, wind cone, wind sleeve, wind sock, windsock | post, stake | blinker, trafficator, turn indicator, turn signal | armband | rocket, skyrocket | beacon, beacon fire | brake light, stoplight | barber's pole ... show more.

is a part of: visual communication.