This offer is only for those with a Kindle with Special Offers (including any Kindle Touch or Kindle Keyboard that opts in to Special Offers, but not the Kindle Fire with Special Offers):
Get $30 Off a Purchase of $100 or More in the Amazon Denim Shop
Click on the offer, then click on the link on the offer page sign up and you'll get an email(right away) with the promotion code. This offer is good for one book and only one per account (if you have multiple KSO devices, they need to be registered to different accounts before you sign up to get the promotion code emails; every Kindle on an account gets flagged when you sign up for the special offer and they will all get the same code for that promotion from then on). Sign-up for this offer expires October 21, 2012, and the promo code must be used by October 28.
The email will contain a link to the promotion page. You'll need to add the items you select to your cart, then use the full check out process and enter the Promo code on the summary page (it's not automatic, like the Kindle Fire promo).
Other than the dates (and getting a code via email, rather than an automatic credit via AmazonLocal), this is the exact same offer that those with a Kindle Fire with Special Offers received a couple of days ago. There doesn't seem to be any reason you can't take advantage of both offers, if you have a lot of denim to purchase, but they can't be used on the same order, of course.