Not really a forum topic but someone may find this useful. Dont think you need to opt in. Limit once per card.
Cardmembers will earn 1,000 Bonus Points when three separate transactions, each to the value of AU$50 or more, are made in Australia at 'major supermarkets' (specified in Clause 1) in Australia during the Promotion Period. Eligible purchases must be charged to the specific David Jones American Express Credit Card issued by American Express Australia Limited ("American Express"). A maximum of 1,000 Bonus Points can be earned during the promotion.
http://www.davidjones.com.au/images/Tile-Images/DJF0024_Tile…