The most common defence signal is Attitude: High to Encourage, Low to Discourage (HELD).
However, there are some situations where it is clear to both opponents that it is pointless to try to give an attitude signal, and in these cases, you can sometimes give a Suit Preference signal.
The hands in this talk are:
https://tinyurl.bridgebase.com/2p89b6h7
https://tinyurl.com/y6xv4h3r
https://tinyurl.com/yyr7l9nx
http://tinyurl.com/y6wym58t
http://tinyurl.com/y87f6xs7
https://tinyurl.com/25c7s62s
http://tinyurl.com/ybauqur9
