American Sign Language
Presumptuously, it's a transformation of a sign 'Good' to 'Luck' in this backward order.
Luck <--- Bastardized the word "Fortune" to "Luck" <--- Fortune <--- Good <--- (Alternative #1) Rewarding for speaking correctly hence the gesture for "You speak correctly, good!" (Alternative #2) A gesture for warm air out of mouth which indicate that it's "good". (Alternative #3) Affordable to buy food. Mouth for food to eat, hand downward for a gesture of holding a bag of money.
Look at each international sign language for the transformation of the word "Good".
French: "Bon" - http://media.spreadthesign.com/video/mp4/10/14618.mp4
Spanish: "bueno" - http://media.spreadthesign.com/video/mp4/5/14611.mp4
Ukrainian: "добро" - http://media.spreadthesign.com/video/mp4/31/110480.mp4
Polish: "dobry" - http://media.spreadthesign.com/video/mp4/19/59015.mp4
- This one-handed ASL sign is produced as follows: