ADJ

clear, unmistakable
agreed, pre-arranged
conflicting, confusing, contradictory, mixed
wrong
Laughing when you should be crying sends out the wrong signals to people
alarm, danger, distress, warning
hand, non-verbal, semaphore, smoke, verbal, visual

VERB + SIGNAL

arrange
He had arranged a signal for the band to begin
give (sb), make, send (out)
When I give the signal, run!
interpret (sth as), read, see sth as
The remark was seen as a signal that their government was ready to return to the peace talks
pick up, respond to
Interviewers quickly learn to pick up non-verbal signals
act as
The insect's bright colours act as warning signals to its predators

SIGNAL + VERB

come from sth
trying to read the signals coming from the patient
indicate sth
the signals that can indicate danger

PREP

at/on a ~
At a pre-arranged signal, everyone started cheering
~ for
She made a signal for the car to stop
~ from/to
Wait for the signal from the leader of your group

ADJ

railway, traffic

VERB + SIGNAL

operate

SIGNAL + VERB

be (on) red/green
The traffic signals were on red
fail

SIGNAL + NOUN

box
failure

ADJ

faint, weak
strong
high-frequency, low-frequency
acoustic, analogue, audio, chemical, digital, electrical, electronic, light, radar, radio, sonar, sound, television/TV, video, wireless

VERB + SIGNAL

carry, pass
The nerves carry these signals to the brain
convert (sth into), scramble, unscramble
The signal is scrambled into code before it is sent
emit, generate, send, transmit
detect, pick up, receive, respond to
This equipment can detect very low frequency signals

SIGNAL + VERB

travel
A light signal can travel well over 16km before it halves in intensity
fade

PREP

~ from
a faint signal from the satellite
~ to

ADV

frantically, wildly
She signalled frantically to us

PREP

for
He raised his hand and signalled for the waiter
to
She signalled to the bus driver to stop

ADV

clearly
These changes clearly signal the end of the welfare state as we know it
effectively
not necessarily
A change of mind in one instance does not necessarily signal a change in overall policy