How To Word Thank You On Sympathy Cards?

You may write,” Your kindness and support was greatly appreciated.  Thank you.”

"Thank you for your kindness in this my time of need."
'Your caring and kindness touched my heart in my time of need.'
'Your caring gift of kindness touched me, thank you so much.'
'You concern was heartfelt, and I thank you so much.'
'Thank you for your words of caring and encouragement through this difficult time.'
I'd write something like these or a combination there of.

Thank you for your thoughts and prayers.

Depends on what you want to Thank the person for...But a simple Thank YOU is always welcome

Do you mean thanking someone for their sympathy? You can say, "thank you for your concern and care, it has meant so much to me/us" Or do you mean thanking someone's family member/friend who has passed as in, "Thank you for the gift of friendship and kindness ________ gave while they were on this earth, it truly touched me."

Your thoughtfulness is very much appreciated.