"signal" - key terms from Wikipedia

analog signal
audio signal
block signal
cab signal
chief signal	officer
clock signal
control signal
digital signal
digital signal	processing
digital signal	processor
distant signal
distress signal
electrical signal
federal signal
hand signal
home signal
input signal
main signal
optical signal
output signal
radar signal
radio signal
received signal
signal
signal	battalion
signal	box
signal	brigade
signal	company
signal	corps
signal	handler
signal	hill
signal	iduna park
signal	integrity
signal	mountain
signal	officer
signal	processing
signal	processor
signal	publications
signal	regiment
signal	squadron
signal	station
signal	strength
signal	transduction
starting signal
stop signal
threat signal
time signal
traffic signal
turn signal
video signal