As the 1918 handbook said, "When a Brownie shakes hands with another Brownie, or with a Girl Guide or Boy Scout, she does so with the left hand. That is the secret sign of brotherhood between them all.
Then also as a Brownie you must understand and be able to make the salute, which is done by holding up your hand with two fingers like this picture.
The Salute is another sign that you are a Brownie, even though you may not be dressed in uniform, and that you recognise the person you are saluting also as a Brownie.
If she is an ordinary Brownie like yourself, you only raise your hand as high as your shoulder; that is called the half-salute. If she is a Sixer, or Leader, or a Guide Officer, you give her a full salute, which means you put your hand to your hat." The two fingers represented the two parts of the Brownie Promise - "1) To do her best to do her duty to God and the King, and be loyal to the Law of the Brownie Pack. 2) To try and help other people, especially those at home."
In 1968, the Brownie Promise changed from two sections to three, and as a result the Brownie Salute changed from using two fingers to using all three middle fingers. And the 'full salute' was dropped, and the 'half salute' became the Salute used for all occasions.