The signal for help consists of a simple hand movement: The person raises their hand with the palm open and the thumb pointing inwards. They then close their fingers over their thumb to form a fist. This movement discreetly signals that the person needs help.

Photo: Signal for Domestic Violence / Source: https://www.worldbank.org/en/work-with-us/hsd/home/signal_for_help
How to perform:
- Raise your hand with your palm open and your thumb pointing inwards.
- Close the fingers over the thumb to form a fist.
The video on YouTube at this link shows the signal in action and illustrates how to perform it correctly.