The attitude signal is defensive technique used to encourage or discourage partner from continuing the lead of a suit.
A 3 doesn't look like a high card but nobody can deny it's a higher card than a 2. Your opening lead is the AH, partner plays the 3 and you can't see the 2. Looks like partner has started a high-low sequence.
On this hand, that's all the information you need to know what to do at trick 2. And trick 3.
Defence in bridge is fun when you and your partner are working together.