Organ is a natural sign, quite similar to piano. Take your two open hands, palms facing down and fingers spread out. Then pretending you are seated before the instrument, start running your fingers sideways, back and forth, as if you are simultaneously playing a two-tiered organ.
Teach your baby this sign when you are attending a religious service in a traditional chapel or church and there is an organist playing.
It is great to teach your child the musical instrument flash cards early on, particularly if you belong to a musical family and would like to introduce your child early to their hobby possibilities.