What is the proper etiquette of sending a sympathy card to a family member?

The correct etiquette for sympathy thank yous (for flowers or just cards of sympathy) is to send cards back to the people who gave you either flowers or a card and add a little note at the bottom of the verse saying you appreciate their support in your time of need. However, it's not always necessary and at a later date when the person is over their grieving they can thank the persons by phone.