knocksignal
nounUK /ˈnɒkˌsɪɡnəl/
US /ˈnɑːkˌsɪɡnəl/
A knock signal is a special knock you make to tell someone something.
The spy gave a quick knocksignal on the door so his friend knew it was safe to open.
OTHER MEANINGS
2. A pattern of knocks used as a secret code.
They agreed on a knocksignal to meet at the treehouse.
3. A sound made by knocking that sends a message.
The knocksignal from the kitchen meant dinner was ready.
4. A way to get attention by knocking in a certain rhythm.
Her knocksignal told the class the teacher was coming.