Signal made by one's nose (6)
I believe the answer is:
hooter
'nose' is the definition.
(hooter can informally mean someone's nose)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for hooter that I've seen before include "It makes a loud noise" , "Uphill stone pusher (Gk. myth)" , "alarm" , "One scents" , "Factory siren" .)